Thank you for playing the game!
Actually I tested the game in difficulty Lv1, without any upgrades or units over Lv 15.
I made hard modes / items and levelups as a kind of 'extra mode' for people who loves leveling up, so I don't know how broken the hard mode is, nor I have plans to rebalance it. :0
But yeah, adding a feature to get rid of unnecessary items might be an option. Hmm.