I'm not concerned about the delay. I did feel it would be good to provide something for potential buyers to use as feedback for whether or not the game is worth it.
I understand wanting the game to be difficult. It's just that when the player's success is consistently based on RNG, rather than skillful resource use, the player is way more likely to feel like it's not worth trying to play further. The boss who can out heal the ultimate sword skill is a prime example of "this isn't fair, it's not fun".
I also understand the combat style of "A Succubus will eventually drain you enough that you can't win". I just feel like that should be slowed down a little, making it less random whether or not the player can win and giving them more time to find the weaknesses of their enemies.
I do want to suggest that you include a boss who can grow many times. This is mostly for "let the player enjoy the growth mechanic" and providing a different sort of challenge. Rather than trying to end a fight as quickly as possible (by killing the enemy), the player allows the drain and tries to last until she is sated (reaches maximum size). This could even be expanded to have 2 succubi, one for breast and one for ass, who you can fight in a 2 on 1 battle too. Satisfying both in that handicap battle will result in the player obtaining extremely powerful gear.