The short answer is, there is no such thing as too much diversity!
Especially when authorship comes from the community being portrayed. So many times mainstream (i.e., white) writers/producers/publishers will look at diversity in terms of matching percentages. So if black people make up 12% of the US population, then make 1 in every 8 characters black (mostly in the background, and lower that percentage because what they really want is what they see in mostly white spaces). Other times, a creative team will include one of everything (from a short list) and pat themselves on the back.
But when non-mainstream characters are dropped in like chocolate chips in cookie batter, you don't really see them. Real diversity is about communities and cultures, not individuals. Sure, keep the individuals, but don't stop there.
When writers of color make their whole world look like them (or at least as the majority), something magical happens. Temper, Afar (comic), Kintu, The Hummingbird's Daughter (all these have a fantasy theme). Other stories are set within minority communities in a white country or are about another country, or set within non-mainstream communities that live in a straight and otherwise mainstream location.
The long answer is, sometimes authors try too hard.
Sometimes you want to highlight a particular community and that's totally cool. Other times you're trying to set a work within a larger community and you find yourself highlighting diversity in a way that overshadows the larger story.
I'll give an example from my own novel. 18 kids from the US time travel to ancient Egypt just before the start of the Exodus. Race and ethnicity is a huge part of my book. Those ancient Jews were not white and a lot of them were of mixed ethnicity. Plus there were a ton of converts from all sorts of backgrounds. My main character and her brother are 100% European Jewish. All the other kids are 1/2 or 1/4 Jewish.
My top characters include a brother and sister who are half black and half Jewish. I also had one sibling group that was part Mexican and another sibling group that was part Native American (they're from Arizona where both those groups are common). This added up to 9 kids who were in part not-white. Half of the total.
If I was just writing about these kids I might have left it as is. The problem is that it was important to my story to have the mostly-European travelers contrast with the Northern African/Middle-Eastern locals they hung out with. So I made the 1/2 Hispanic kids 1/4 Native American instead and made the formally 1/2 Native American kids 1/2 white (non-Jewish European). Now it's 5 kids with a non-European ethnicity.
I still have plenty of ethnic diversity to work with. Because it's mostly with the ancient Hebrews, it works even better to teach the travelers how to overcome their American ideas of who counts as a Jew and how race intersects. I couldn't have done that as well had half the kids been of color.
Gender, sex, and sexuality.
I struggled as well with lavender representation in my story. As I belong to this community myself, I have no desire to write a book where everyone's assumed to be straight. On the other hand, it's an upper middle grade novel. The oldest main characters are 14 (8th grade) and none of them are dating (yes I know sometimes kids that age do date, but mine haven't started yet).
The ancient Hebrew group has marriages and family units around traditional gender expectations. People weren't any less likely to be queer back then (you don't get a ton of rules against something that isn't happening), but it manifested in ways other than family structure. But since I'm focusing on kids (my MC is 12) and writing for kids (upper middle grade is about 8-12 years). And since I want to concentrate on issues of faith and ethnicity, I'm downplaying it all.
I'd be lying if I said I had no mixed feelings, but I am okay about it because it works for this story. If I told the story from the point of view of an older teen or an adult, I might showcase some very different things.
Just because I choose not to tell their stories doesn't erase their existence.
Duh, of course some of my characters are lavender. I didn't sit and try to figure out who; I asked them. (Yes, I'm in the stage where my characters tell me who they are.) Of those 18 kids, 2 grow up to be gay. One is 2 at the time of the story and the other is 14. The 14 year old is my favorite character because he's very complicated (and a total jerk). I show him with his husband and son in the epilogue when they're all grown up. Otherwise, it's not stated in the story. But is it there? Of course! I know what's in his head. I see how his eyes linger on certain young men. I feel his heart beat out of his chest when he's with his new best friend who is from Egypt. Readers who look for it will see it too.
So what about your story?
If it works for you as an author and it works for your story, then have them be who they are now. If it feels forced to you, then make some changes. Next, ask some beta readers or a writing group what they think. I did this with my spouse, whose comic book series just published its second issue (of 20). That story is an explosion of diversity of every kind. So when he told me he thought my US kids should be more European (for the reasons I stated above), I trusted that.
Will you alienate some straight white readers with your story? Yes. Yes, you will.
But every story alienates someone. I posted a couple questions about my story over on Worldbuilding and was shocked at the things that caused people to hate my story without ever having read it. My older kids weren't adult enough; they should take on adult responsibilities. My older kids were snot-nosed brats who couldn't possibly be helpful in any way. My MC couldn't be a leader because she was a girl. And so on.
And ya know what? It's okay. You can't make your story right for everyone. Make it true to yourself and make it publishable.
If you're honest with yourself and find that you're adding diversity in a way that doesn't work for your story, take it out.
If you find you're taking away diversity in order to appease imaginary readers, put it back in.
Find your balance and tell your story.