Well, "new and interesting gameplay" is largely separate and distinct from the choice of leader to my mind. Civ VI doesn't has veered away from using civ's as a way to offer a highly asymetrical playstyle. Rather, they toss hodgepodges of production bonuses, district adjacency bonuses, yield bonuses, unit experience bonuses, temporary combat bonuses a after DOW blah blah blah.I'm glad that not all leader decisions are popularity contests. I'd much rather get fresh new faces with new and interesting gameplay rather than rehashing the same "iconic" leaders over and over again. Plus, seeing new leaders provides a way to learn about facets of a nation's history which may I may not have known.
It's interesting that all the largest outcries (Cleopatra, Catherine, Seondeok, Jadwiga, and now Kristina...am I missing any?) have all been over women... even though these are all women who actually ruled the nations they're representing in Civ 6.
More to the point, it's not about new faces versus old so much as it is about choosing noteworthy leaders versus unaccomplished leaders. Longtime fans of the game see Civ as a kind of all-star game where great leaders pit great empires against each other. An all-star game is, by definition, exclusive and elitist. This has been decremented over time, with civ's that don't qualify as empire-builders showing up, trickling in slowly and now flooding in as "diversity" has become the loftiest of mantras and the most (self-)back-pat-worthy goal of any earthly endeavor.
Now, as is often the case with diversity initiatives, some people will desire that meritocratic standards be maintained. If a leader for Rome isn't one of The Five Good Emperors, it ought to be a damned good candidate all the same, rather than just picking that candidate for its "otherness". Same goes for bumping a well-known empire for some obscure niche nation. Prioritizing some postage-stamp city-state or subsistence-existence tribe over, say, the Mongols, doesn't sit well. Some get their nose out of joint about that, and the reaction from others is that the preference for exclusivity is a canard borne solely of misogyny (or racism or Eurocentrism or what have you). Doesn't help that sometimes such an objection really does come across that way. Or, if we really are going to be honest, some of those founding all-stars perhaps weren't all that deserving.