I'll side with your editor. Why do you need two jolly characters, or two stern characters? I wouldn't worry about mannerisms, I am more interested in purpose, intent, attitude and conflict.
I think you make it hard for two characters to be in conflict, and hard for two characters to have plausibly complementary skills (for synergy and needing each other) if they are too alike. Minor difference don't count.
You don't need to hammer readers over the head if you make them distinct. Roll your jolly characters into one; roll your cynics into one. A cynic and a jolly character can have synergy, at times one succeeds in a negotiation, at other times the stern cynic will succeed when friendly banter fails. At times brains beats brawn, at times brawn pummels brains.
Also, if your crew has only one of each type, disabling the one causes them hardships through the loss of that talent, an obstacle to overcome.
Your story should be efficient, only as many talents as you need and no more, and no duplicates. If you have a lot of the same type of character (eg "soldiers") then I'd keep them nameless and faceless until you need a specific one.
Also, rolling two same-talent same-personality characters into one will let you paint a richer picture of that one; instead of splitting time between two shallow versions of the same thing (and causing confusion).
You have the right idea to show personality through action. Do not avoid showing it through dialogue; much of personality is opinions, sometimes intelligence revealed through word choice or the complexity of sentences. Just keep any explicit statements (tellings) of life philosophy to a minimum, or somewhat cryptic: "Yeah, well, I don't believe in that. It's wrong." Without expansion or explanation. The kinds of things we actually say.
Characters do not always have to be extreme to make them different. IRL some are liberal, some are conservative, some are politically ignorant. Some are atheists, some are devout, some (male or female) are more promiscuous than others, more outgoing or shy, more selfless or selfish, more shallow-thinking or deep thinking, more analytic or more reactive, more talkative or quiet. More or less educated, more or less talented, more or less wealthy. Just make them distinct.