Thanks for the feedback!
It's true that the game can be slow/fast depending on which upgrade was selected. I guess it's the tradeoff of not having a completely linear upgrade tree.
I wish I could find a good solution for the grinding-previous-level. It somethingthat annoys me but it's the downside of how the map is done (ex: having a forest level). I tried to fix this with some upgrade to the hermit "wild growth" but it's more like a patch fix.