I 100% agree, in this idea most players would be stuck in a roadblock. They can't progress in the game until they perfect landing and returning in all planets. This won't work at all, why? Because it took me 160 hours for a Mun landing.
Now imagine for a harder planet, i.e Duna, you have to get to to advance in the game. Players would be stuck, not able to advance any of their tech until they can land on another planet, and that could take..what? 200 hours? 500? its extreme and would ruin the whole game of KSP.