I didn't play the hack at all, but from what the removal log says, the level design could be improved if you played with resources a bit more and implemented some challenge. And since the levels feel like "gauntlets", cutting down their length would be beneficial for the gameplay to not turn out hectic and uninspired.
Protip: if you want to keep longer levels, be sure to not make them too jarring and introduce midpoints per half. By no means you should utilize every screen the editor offers, but some sense is necessary here.
As for the Wart boss, if it was a Hard hack I'd keep it in world 1 but make it less harsh, but since it's supposed to be a Normal hack, I'd introduce it some worlds later due to his patterns. In fact, it can be buggy at times. I'm usually not a fan of harder bosses early on.
As for sprites: I agree, introduce them in a friendly way and not in a bullet hell fashion. I don't mean they should not be used, but: their usage should provide more action and movement from the player as their appearance goes on.
As for slowdown: have you considered using
NMSTL or (in the more extreme cases)
SA-1? If that's not the case, do it or trim down the number of sprites per screen.
I think that's all. Best of luck with this!
Windowless ride, feeling alive
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