Lol I've never beaten Sephiroth either, tbh. In my second playthrough I managed to obtain every single materia, but the grinding required to master them all was far too daunting to do alone. At this point there are so many extra things to do in the game that I can't be arsed. I did almost everything the second time, got all the enemy skills, won all the chocobo races, got all the good Battle Square prizes, bred all the chocobos etc. During my latest playthrough I was trying to beat Ultima Weapon and having trouble finding him, even though I've beaten both him and Ruby before. Speaking of Ultimate Weapons, I only recently learned that they don't allow materia equipped in them to gain any AP. I never even knew before that different weapons have different rates of AP, and I've since sold all the weapons that might have been superior in that regard. You'd think Ultimate Weapons should have great AP rates considering they're so hard to obtain.

But yeah, I may just cave in and forget about the Weapons this time and finally finish the game. I've never seen the ending, and I don't want to watch it on Youtube. I don't think I would have enough patience to master all the materia or do any of the extra stuff at this point. Playing it again I've realized how much smaller the game is than I remembered it, and it just doesn't hold the same appeal anymore. Good on you for finding so much to do in-game, but I would urge you to complete it eventually - as you've said, you won't find closure otherwise.