I understand it's not a game to just go through and beat. I want to beat the game so I can have the best spells equipped and go for the Avalon Pacts. However, just to get to that point, it feels like the game is a slog. I'm on Chapter 2 of Fading Humanity so I think I'm getting towards the end?
Delta is easier to get things all around so you won't have tough time getting best spells. In SS, many magics/spell offering have broken balance thus many of them aren't very good all around but the Delta will fix all these problems. The devs have changed and tested out throughout the patches for the right balance therefore you wont have tough time as a new player or for one who imports the save file. You can pick up where you left off.
also in SS, even if you destroy parts - the spells may not drop at all but in SSD you'll get it all times. Those Avalon Pacts are now just "Pacts" in SSD - this is part of game that you don't even have to do - in Delta you have twice if not triple more the content in this category and all can be done solo.. That's not the main attraction though, its the lore, the magic and setting.