big disagree here with many:
So the game is Civilization, not Leader, so to me it's the civilization which should last forever but the individual leader who change from time to time.
I guess you do lose some sense of familiarity if the other leaders change in mid-stream.
But by that same token, you are also still playing civilizations which often historically did not belong in the era that you're playing. Apples and oranges.
Perhaps you could allow leader switching, but in the player banners you could display the previous leader grayed-out next to the current one. So you don't forget as easily. Might take up more screen room but that's a UI design problem.
Doing it the other way around doesn't work and is worse in many ways, unfortunately.
Firstly, leader swapping puts the ENTIRE focus and decision-making on what
leader you'll play as next, and not what Civilization. Changing Civs inherently makes you think more about the Civs themselves, their pros and cons, and their synergies, while your leader is a passive constant helping you in the background.
Secondly, creating a leader is much more expensive than designing a Civilization is. Every leader is 3D animated and voice-acted, in the closest approximation of their native language possible. Designing a roster of 10 leaders per Era and 21 playable Civilizations (with temporal variations) is more expensive and could put the devs in problems with their publisher who wants their deadlines to be met.
Thirdly, not every Civilization is created equally if you want Uniques. America's uniques kick in much later than Egypt's or Rome's. Antiquity-fronted Civilizations will start the game by building up a lead, forcing the later Civs to catch up. You can use your leader to stay level but what isn't to say Rome or Egypt wouldn't use the same leaders to extend their lead?
Finally, Civ's USP over other 4Xers has always been its distinct Civilization flavour - the music, the unique units, the art assets. All of those are present in Civ7, within their confined era.
It's far from an
ideal approach, but I understand why it was taken. It was for the sake of making every Civ in the game feel relevant when they were at their historical peak. The decision to confine every Civ to a specific era ultimately benefits the
Civilization itself the most, and that's within the spirit of the game.
There are things that concern me about Civ7, but the Civ-swapping itself has never been one of them.