its ok i appreciate you coming back to comment again :)
unfortunately we only really had time to let 1 person playtest before we had to release the game, and the 2 bosses you disliked were the ones they kind of just steamrolled, so we really didn't have any chance to get valuable feedback on those.
as for the cube boss, his main attack does have a bit of windup and his other move only happens ever few attacks, but those are definitely things that are easy to miss and would greatly benefit from at the very least being more obvious, he was very rushed though.
there is some cool stuff after him but I don't blame you for wanting to stop there.