In creative actiivies like game design all rules are simply guidelines, to be ignored when necessary.
A good thing to keep in mind, though, is that successful designs need fewer changes than unsuccessful designs. As in, Civs IV - V - VI were all increasingly successful, so radical change was not necessary except to salve a designer's ego.
Whereas I would suspect that Humankind II will be radically different from Humankind if anybody expects to sell it.
Further, the parts of a design that get the most negative comment are the ones to look at changing, one would think.
From that standpoint, while there was much discussion of the Eras/Ages, nobody (as I remember) ever said they were game-breaking, merely that there might be a better way to organize the gameplay. Also, while there has been much discussion of Civ transitions in the game since at least Civ IV, after Humankind I don't really remember anybody arguing that Civ Switching was the only way to play.
On the other hand, 1UPT got a mass of negative commentary (and some positive, to be fair), but is still with us.
Religious Missionary Swarm was widely negatively viewed, but is still with us.
Makes you wonder about the decision processes involved in Civ VII's design . . .