Just finished the game, it was actually quite fun and challenging ! I think there's more to do with the powerups but that's a great starting point/proof of concept !
I tweaked it multiple times to get the right difficulty but yeah it still needs a few adjustements.
As for the nav mesh, it clearly is the biggest issue I faced. I really struggled with Yahaha to get the movements working well. I'll keep trying tho, thanks for your comment.