I won't deny Disney deserves a share of the blame, but naturally, if you're gonna agree to co-finance the films (whereas before, the MCU Spidey films were fully financed by Sony with Disney getting a small 5% cut of the box office revenue), then you're gonna want a bigger share of the profits. Unnecessary? Maybe, but it now looks as if Sony simply were the ones not willing to play ball. Whereas before, it was reported that Sony was willing to keep the past deal and Disney instead wanted that ridiculous 50% cut, it's now being reported that Sony didn't give Disney ANY counter offer to their much more respectable 25-30% cut and simply weren't gonna accept or even listen to any offer, which goes back to my point about Sony suffering delusions of grandeur.
Both sides look bad in this, but Sony aren't exactly a reputable studio, so they're in no position to play hardball. They haven't made a good live-action film without Disney's help since 2004 (I actually quite enjoyed Far From Home). It was they who shoehorned Venom into Spider-Man 3, causing it to be a bloated mess and ran both Spider-Man and Ghost Rider into the ground with the horrendous TASM movies and the 2007 movie and 2012 sequel, Spirit of Vengeance, respectively.
The rest of their portfolio isn't great, either with so many sh!tty films like Ghostbusters 2016, Emoji Movie, Men in Black: International, Aloha, The 5th Wave, White House Down, Total Recall, RoboCop, Red Dawn, Paul Blart: Mall Cop 1 and 2, the Paul W.S. Anderson Resident Evil movies (the first one was alright IMO), The Dark Tower, Spectre, Pride + Prejudice + Zombies, After Earth, Pixels, Sex Tape, Jack and Jill, Grown Ups 1 and 2, and Ghost in the Shell, hardly a boastful list.
Yeah, they make the occasional good film like the first and third Daniel Craig Bond movies, Whiplash, first few Underworld movies, Superbad, Blade Runner, Jump Street movies, Into the Spider-verse, Girl With the Dragon Tattoo, but they make a LOT more bad than good.