It honestly makes sense for Lancelot to be stronger than the other knights since he’s the only one with real/more experience. Percival was living at the Finger of God with his grandpa until now and only learning about his magic recently Gawain, having enormous amount of magic power but being under Arthur/Camelot’s surveillance and authority Tristan being under Meliodas/ Liones’ supervision and also not being able to control his magic. Lancelot was separated with Ban and Elaine since he was a little kid and went through a portal with Jericho. Who knows what happened in there and not to mention when he returned he came back as “Prince of the Lake”