Even if they're bad at using the weapons, which makes sense considering nobody received any legitimate training, the technology shouldn't change.
Kylo should have killed Finn in TFA. The guy lost his spine. Lightsabers don't rip clothing.
Rey should have taken at least half of Kylo's face off in TFA. Lightsabers don't give tiny scars.
In TROS, Rey should have severely damaged Kylo during their duel. You don't just stab someone with a lightsaber and leave a tiny hole, unless you mean to. If it was the result of accident, he would have died.