They're both important given the situation. Why focus on either/or? There are spots where you need to have a good opening jam range/3bet jam range/4 bet jam range that puts you in a +EV situation. There are times where you'll need to able to fold in key spots preflop, flop/turn/river based on a ton of variables. Both go hand-in-hand. Someone might say 'you can't win a tournament if you cant fold and get busted out', but you can't win an MTT if you are accumulating chips either.
If I'm being honest, a lot of weak/tight MTT players in the microstakes are often folding way too often in spots they should be jamming. I see them all the time only open/3bet jamming with the top of their range and folding everything else. Sometimes to the point where they're they have 2BBs UTG and they fold J2s because it's too weak of a hand.
Folding is easy. I see the same weak/tight microstakes players doing it all the time and they're super exploitable. If they don't have a good preflop hand, fold. Miss the flop, fold. Check raised, fold. Thin
bluff, fold.
So, in this situation, for most weak/tight players, jamming is harder than folding.