I'll point out some nuances that address your question, but they won't give you simple yes/no answers.
...born with powers in a family full of metahumans (like in that hero
anime where everyone has powers and there's just 2% of people who
I'll start with the biggest issue. Your worldbuilding breaks this entire premise. You have a fantastical world where 98% of people have a physics-defying superpower, presumably all have different superpowers and since almost everyone has them they are 'natural' in this world.
Everyone has Superpowers™ trope, nullifies our current real-world power structures. How long has this been going on? Generations? Always? This world would would not resemble our own.
If you scaled it back (2% have superpowers, 98% are normies) then you can probably preserve the real world. The fantastical has limits. The 'Supers' need to remain grounded to interact with the majority of their friends and family. Many supers would set themselves apart from society, but just as many would prefer to live within normal society, and (by simple majority) real world power structures would be maintained to govern the vast majority of normal people.
More importantly, the 'normie' power structures would touch (if not actually oppress) the Supers. It would effect their friends and family. They would have grown up under Normie power systems until they reached an age where they might decide to reject Normie rules.
By pushing this worldbuilding aspect to 11, you've drowned out any nuance that might be in play if you dialed it down to a 2 or 3.
It's gritty, and real, with real characters who have real emotional issues that are relatable....
Except it isn't. Everyone has very UN-relatable superpowers that defy physics. Everyone is extremely UN-real, with magical abilities to solve all their problems. No one is 'stuck' living in the ghetto. There are no superhero have-nots. The government cannot oppress any group, the majority cannot exploit a minority, dominant groups cannot point a finger at sub-classes when any member of that subclass can BLINK their oppressors into the next dimension, or toss them into outer space.
Bullies would not survive elementary school. Parents would not survive having teenagers. Road rage would remove a large percentage of the population.
Resources are not attached to superpowers, neither are economics, or race, or gender. There are no strategic levers to oppress entire groups when 98% of those groups can defy physics. There can be no 'real'.
It's the same trainwreck as the worldbuilding, except here it's not a broken world, its a broken story. What are the stakes in a real-unreal world? Who is the market for 'gritty and grown-up spandex-wearing magic super comicbook costumes...
If this story is for children, everyone is super-magical, and magic solves all plot problems. Unlocking new magic powers is just 'leveling-up' like a videogame.
If this story is for grownups, magic does NOT solve problems it creates conflict and alienation. Unlocking new magic powers involves moral compromises and sacrifice.
This is a theme conflict. You've got rainbow unicorn stickers in your brutal noir. Think about what you want to say with this story. If it's a fun rivalry between super-friends, stick with escapist fantasy and avoid the ugly, gritty, real-world stuff that people read escapist fantasy to escape.
Stories should not try to be all things. You have a fantasy world where everyone defies physics. It's not a leap to say everyone defies racism/classism/sexism/prejudice. If this is not part of your story, leave it out. If you feel that makes the story too 'unrealistic', like everyone lives in happy Disneyland, re-think the part where everyone has magic superpowers. This story is already 'too unrealistic' to support dark real-world themes.
With the right balance you can have both co-existing, but you'll need to understand what you're trying to say. Only then you'll know if (specific aspect of gritty reality) fits within this story's theme.
Typically you want to balance your characters. With a lot of power comes some sort of burden or responsibility.
Too much power and the character is no longer human –– like how Superman evolved over decades from a circus strongman in the 1930s, to 1950s smallville dating hi-jinks with Lois and the gang, to immortal abstract spacegod by the 1990s. An energy-being with limitless power doesn't fit in children's stories about a strongman lifting a car, or in 'Lois is trying to trap a man' comics. His eventual limitless powers are way out of scale to these earlier plots..., hinting that he didn't have those powers when those plots were written, and a lot of ret-con has been done to keep this character from accumulating all this silliness.
With even a little bit of power, any character would be tempted to use it – just this once – to cut corners, to tip the scale, to not lose. DC solved this quandary in Superman by making him not human at all. He's a space alien now. Problem solved. Throw that whole 'relatable' out the window forever, we can't go back to dating shallow Lois. It's a slippery slope, and might makes right when the 'might-o-meter' has been dialed to 11. Superman doesn't need Jimmy Olsen as a friend, there are bigger problems in the galaxy.
Again, keep it in scope. Watchmen works because that world of superfriends is a hotmess of psychological disorders, narcissism, and character flaws. It's a worldbuilding trainwreck that leads to... a very broken world. We're not suppose to like the characters in Watchmen, that's the whole point.
BUT... I want to point out that Superman as circus stronman was the appropriate character, balanced for that era and reader. Marriage-minded Lois (or her cousin stand-in) was the readership in that era. Superman was again 'balanced' in the '90s for a critical older readership, both through cannon, and in parodies like Watchmen.
Microaggressions are a thing we understand today.
There are probably ways to keep them micro, that could inform the reader about how that character thinks, and how he views the world and his rival's privileges.
It's up to you, the author, to show through the narrative whether he is wrong or right, whether he's feeling sour grapes, whether his rival registers the microaggression for what it is, and how he deals with it.
YES you should investigate using microaggressions to inform us about this character. Make it clear it's the character and not the author, no one will get confused.
Keep the microaggression micro and let the situation play out for micro character conflict. Is this enough to make Character B allow Character A to die...? No. But it's enough to let Character B know what type of person Character A is, and that should have a pay-off later... a micro pay-off.
Character A could be an Archie Bunker or a Homer Simpson, he'd be dropping the microaggressions right-and-left while we hope he manages to at least work out some of his macro-problems. In this case the microaggressions should be patently wrong, they are a part of his ignorance as he mangles incoherent prejudice with sour-grapes and wishful-thinking. He could be an unreliable narrator, and the story-world shows us differently.
Race-casting and undermined power structures
In the US a common movie trope is the 'maverick cop' who is a crazy-like-fox underdog in the story, while being cast as a handsome white leadingman™ actor.
To help diversify the cast, he will have a Black partner and a female boss – possibly a Black female boss – and the handsome white male leadingman™ will undermine the authority and autonomy of these other (minority cast) characters. She is his boss, but she is wrong. Her authority is dismissed without consequences. He drags his partner into danger, but it's not 'wrong' and that character is in service to the white leadingman (despite them being 'partners').
Race casting informs the viewer. It's intentional. It's actually cliché and soft white supremacy. It's also how commercial cinema works. Audiences like the white leadingman, and they like seeing him be right, and they like when he wins. I don't know your story or how the conflict between Character A and Character B plays out, but unconscious bias is something we all have, writers and readers. If your story 'proves' Character B to be 'wrong', were you playing into this bias?
Did you give Character B extra points (money, privilege) to show that these things don't fix the flaw of being half-Black? You cannot be un-aware of the trope where half-races are dishonest and immoral and tragedy-prone. This trope is ingrained in Euro-white operas, classic novels, theater and film, pulp stories, etc.
It's not an excuse to say 'I am also a type of minority...' because colorism, and nativism, blood-purity, and intersectionalism pre-date the concept of microaggressions. No one gets a pass because of ethnicity or skin color. We live in a racist society and power structures exist. No one is immune.
But it's not your responsibility to fix the world. Just write your story. Lots of these character questions will come up, and my suggestion is to not be afraid to show some dark corners in your characters. Let them say stuff they don't mean, give them something to regret, allow them to make fools of themselves –– that kind of character doesn't fit every theme, but everyone (even kids) enjoy flawed characters who get themselves in a hole and have to work hard to get themselves out of it.