Not gonna disregard your take, but my guess is that they need some time to fix some stuff. For example, the stage 5 boss does have an HCG animation, but the boss can't hurt you. The boss when raping the fairy princess will cause a glitch that will drop them at the bottom of the screen. It's about stability at this point and some testing with new content hoping that nothing can go wrong.I hate how the dev is purposefully delaying content to milk the most amount of money out of supporters, there's an hcg animation for stage 4 boss, stage 5 normal and boss.
And get this, stage 5 and stage 6 are fully playable for the exception of not having that "story cutscene" at the beginning of the stages
Again, not disregarding your take. But give it some time. Development isn't easy. I would know, because I am a dev myself. I know that it's the same formula from every stage and every enemy, but they're adding some variety and extra content that the last 2 games don't have.