A fire pokemon is weak to water. That is a weakness. However a limitation is that it can only breath fire up to 9000 degrees. Weaknesses are things that hurt your quirk things that it can't overcome, or things that hard counter it. Limitations are things that the quirk in itself aren't capable of doing, or its upper limit. Much like how Midoriya can break his arms by using his quirk near its full potential pre training.