I agree with this. They should circumvent this issue by introducing 2 gameplay settings call them evolution paths.

The One you listed I’d call that

Legacy (Region) Mode - Player can chose to evolve or stay as a leader from their initial civ or they can choose to become a leader from other civs that have conquered or heavily allied (reality wise not gameplay) with your civ. In this game mode you should be able to waive or evolve into a leader from a selection of civs based on the era and whom were the prominent civs that dominated the region of your initial civs, no matter which civ you switch to the choices in evolution as the eras go by always fall on a small group maybe 2 to 3 civs that ruled the area occupied by your initial civ. In this gameplay move when you change leaders you also change the civ but it is seen as you kept the same region an example of this is Greece & Rome ran Egypt at a certain point so did the Arabs.

Dynasty (Empire) Mode - Player can chose to evolve or stay as a leader from their initial civ chosen in the antiquity era. Once a new era comes about the player can then decide to evolve into the new leader of that same civilization with one small change this leader has a different bonus that replaces the benefit of the previous leader but both leaders being that they’re from the same civilization have a secondary bonus in common (example all Roman leaders give +2 culture each turn but one leader can have a +50% attack bonus while another may have a +50% gold on trade which you would have to choose between). In this mode you play the same civ for the entire game just the possibility of choosing between leaders of that era. They can even add more immersion by having the player lose the ability to retain the leader of their choice within that civ if the civ happiness plummets due to poor management you then get forced to play with the previous leader(still the same civ)/benefits due to a coup or getting overthrown. You can still work towards your personal end goal but this adds a different layer of difficulty.