It isn't necessarily wrong. It isn't necessarily correct either. It quite simply depends on how well the factions are designed around the concept of possible mirrors.V
Does the game become more competitive if balanced mirror matches are included, or just more diverse?
And authenticity? I honestly don't care. Lacking authenticity never ruined Age of Empires 2 or Call of Duty 2 multiplayer for me. I get that some people actually get these kinds of games because they're somewhat historically accurate, and while that's fair, that's what the single player campaigns are for in my opinion.
Do you gain anything apart from more diversity with the addition of mirrors? Is more diversity worth the loss of authenticity? In other words, are mirror matches an objectively superior addition, or truly just an aesthetic preference ("I prefer diversity/authenticity to authenticity/diversity")?
Also, chess would've been mirrors if it wasn't for the fact that it's a turn-based game and thus asymmetrical by default. :V
Exactly, that's one of the really amazing things about chess, it seems shocking that just having one side move first could create radically different play styles for two otherwise symmetric sides (mastering both sides of chess is many times harder than mastering both sides in CoH, I would guess).