Like with a lot with Civ 7, I think expanding the leader selection was a great idea, just poorly executed. I don't understand the idea behind adding leaders with next to no connection with any playable civs. Having the national hero of the Phillippines without the Phillippines to lead is just wasted potential. The same can be said about leaders from civs that were already represented. I'm stuck wondering how we have 2 Americans, 2 Frenchmen, 3 Germans playable when all of East Asia has 4, two of which have no relation to any civs... I can go on and on about this because it bugs me so much (not a single Greek leader?? Simon Bolivar over literally any Mexican figure??) The leader pool feels so limiting at the moment, when expanding the roster should have done the opposite of that
I completely agree with this and you can see the backlash of doing so in the comments of the Simón Bolívar First Look Video on YouTube. I bet Firaxis though that having both Mexico and Simón Bolívar in the game would instantly make all of Latin America happy and "represented", but the effect was the exact opposite. Most people commented that it's a bit weird to link Mexico with Simón Bolívar in any sense, that they hoped they get to have Colombia back as a civ and a separate Mexican leader for, well, Mexico per se. Some comments even get to the point of being angry arguing that "Americans think that all Latin American are the same" by having "Simón Bolívar as the leader of Mexico".
Meanwhile, the First Look video for Gran Colombia in Civ 6 has much more positive comments in regards to representation of the region and even of Hispanic America as a whole, even from people who are not from the countries that descend from Gran Colombia. It's better to have complete representation of a single nation of a region, rather than a leader from there and a civs from elsewhere in the same continent awkwardly linked by the devs in a single package. The game would have had a better impact in Latin America if they had either a Mexican civ with a Mexican leader, a Colombian civ with a Colombian/Venezuelan leader and or a Brazilian civ with a Brazilian leader, not a weird mix of leader and civs as they did in Civ 7.
I wouldn't be inherently against leaders being separated from civilizations. However, it would have been cool that there were at least one corresponding leader choice for each existing civilization within the game, so as not to have this kind of problems of bad historical representation and forced links between completely unrelated leaders and civilizations that can be received badly by real life audiences from said cultures. A system similar to Civ 4's optional game setting that allowed you to choose any civilization and match it with any leader, but still having a corresponding "historical" leader for every civilization.
PS. As a Colombian, it is indeed rather bizarre to see Simón Bolívar's First Look video feature a song that's representative of Mexico in the same way the The Star-Spangled Banner is representative of the USA. That's like having a George Washington First Look video with O Canada! in the background. I bet many Mexicans felt the same. It completely ruins the idea that Firaxis might have had of being more "inclusive" when choosing which civilizations to add to the game.
(The Spanish theme would have suited Simón Bolívar's First Look video a lot better than Mexico's, considering that Spain's theme is based on a musical composition made in the South American colonies by a Peruvian composer and, well, at least Bolívar ruled Peru)