Yes, all these additions can be pretty divisive amongst the fans. But this iteration of the game seems to be more focused on off-beat leaders and their interesting personalities. That is why we have Catherine de' Medici leading France or an entire Macedonian civilization being included for Alexander to appear or Georgia being introduced because Tamar is such a cool leader to have. So Civ6 seems to be the best chance for Mandela, Ataturk and Simon Bolivar to appear.
And they can also bring some interesting, late-game focused elements to the game. Like for Ataturk, modernising and secularising what I think would have been a deeply conservative and religious society like Turkey was no mean feat. And when we have so many leaders with faith based abilities, having one with an exactly opposite focus that steers you away from faith and with abilities kicking on in later part of the game will be interesting.
Also, you can always have an Ottoman sultan as an alternate leader for Turkey as a DLC later on.
As to Simon Bolivar, the political entity that he led might not have lasted long after him, but isn't he considered a founding father of sorts in many Latin American nations?