Pretty much this. Unless season 3 gets some great reviews I won't even bother watching that at this point, much less a season 4.
With a series like this you have to cater to the fandom and stay more faithful to the source material within reason. If the writers had it in them to create a compelling story deviating from the existing lore they would have shown it in the first two seasons. Cavills performance and identification with the role was compensating for some of the flaws in the writing department and generated a sizable share of the hype surrounding the show in season 1. Netflix should just have fired the showrunner instead, if it would have helped to keep its main star on board.