Thank you so much for the kind words - and for the extensive review, this is very useful! I love getting in-depth feedback like this. The grenade is an actual physics object and as such kinda just does its own thing, haha. You can get it to move up by jumping into it from below, which is actually an alternate solution to one or two obstacles (combined with the "Remote Touch" upgrade.)
I have relatively little experience with this sort of game design, so yeah, the boss fights needing some balance adjustments makes sense. The Seal of Disapproval is meant to be an easier fight than the Omega Spamloid, though the difference between the two isn't meant to be quite this big.
As an immediate measure, I've nerfed the Omega Spamloid, reducing the damage output of all the add-ons and shortening the fight timer. It does require some unusual strategies (like taking advantage of the mercy invincibility and accepting damage that you then recover) but I think it was a little too harsh. I'll probably circle back around to this in the future and maybe take another look at the mechanics. Again, thank you kindly!