It feels pretty smooth and I really like the movement overall, but you're right maybe the web version is the problem. It could also be that I'm just bad lol. Maybe a checkpoint once you get to the top of level 4 would make it less frustrating to keep trying.
I myself experienced lower frame rate on the web build which led to some strange behaviour in the game, which is why I thought it might be a performance issue. This game is certainly unforgiving as is, so I don't blame anyone who has trouble with it. We made a total of 17 levels for this game, so if you thought level 4 was tough, you haven't seen anything yet ;)
Thanks for trying out the game and sharing your thoughts!