You won't need to complete the game 20+ times from the beginning to get all the endings; when all content is in, you can use multiple save slots and only pick Ideals from bosses if your goal is to get all the endings, so you'd only have to play from the final boss onwards.
That said, the game isn't designed to expect people to get all 21 endings, as we don't expect people to fully complete all content and it's more about how each person's individual runs play out (and because with 4500+ cutscene variants, true full completion would probably take 500+ hours even if you knew where all the really secret stuff was).
Hopefully though the savescumming trick will make things a lot easier on you :) and glad you've been enjoying the game! Definitely check it out again once the megapatch is in, too, should make things a lot easier.