Ok, I think I understood the tutorial wrong. I thought I need to shoot all 10 bottles but apparently you are not restricted by bottles falling but your bullets. A bit unintuitive but at least the tutorial is a bit easier after realizing that.
Went and replayed the game based on this info. The henchmen levels are maybe a bit dull and they drag out too long. I would have preferred shorter levels as nothing really changes during the level and there is not much challenge. But boss levels are quite fun, I must say!
Updated my rating accordingly. Thanks for the advice!