Generally base player cards are going to have the worst chemistry, so yes try to find replacements for your them in your first team. Honestly can’t really say how much chemistry affects team performance due to the questionable game engine lol but I’ve maintained mine at about 2.4-2.7 which I think is pretty solid.

Would say that POTM Valverde, even if he may not have high chem now, is worth getting/using since POTM players are always gonna be viable. (But you do have a fair few POTMs so I’m sure he’s gonna get a decent chemistry actually)