Wow, so much hatred in this thread, even though the episode wasn't that bad at all. Yeah, Lurantis could've moved a bit more, I guess that's not its battle style though. Venusaur never moves in battles either. The crowdedness of the forest is no excuse to me, Lurantis lives there and is a forest pokémon, it should have adapted somehow. Sceptile is also big but it can still move a lot in dense forests. People say Mallow should've done more, which makes me wonder what role they think she should've played in this episode. This was Ash's trial, not hers. You don't get complaints that Serena didn't do anything in the episodes with Ash's gym battles either. The battle could've been longer, but I think it was fine. As opposed to gym battles this battle was only against Lurantis and Castform, in most gym battles the leader has several pokémon so you change up the match-up every couple of minutes, and filling close to 20 minutes on the same match-up is a bit excessive I think, there's only so much you can do before it gets stale. I like that they dedicated the first half of the episode to gathering ingredients similar to what happens in the games.
I think some people here are also too focused on the game mechanics, even though the anime never power scales the move strengths exactly like that. The anime is more plot-driven than numbers-driven, and it always has been, that's why Greninja could still get away with using Cut at the league last season.