There's no such thing as franchise fatigue. I remember when Critics were saying the same thing about God of War franchise at one point. Nobody ever cares about Franchise fatigue when it comes to Mario, Resident Evil, Pokemon, COD for example... Uncharted never faced having a franchise fatigue as the games are their own capsuled adventure... You can skip one entry and still not be lost, so they never ran the risk of burnout on the end user.
I only mentioned Indiana Jones because thats what the game was inspired by.. an action adventure pulp fiction theme based around treasure hunting, so it allowed them endless material for story concepts.
Drake's personal story was never at the forefront till Uncharted 4 that's my point. His "story" was always about building his own legacy until Neil retcon'd that arc by rewriting his origin to fit in Sam