Sony cooperating with Disney on MCU Spiderman films means that we get MCU Spiderman AND Into the Spiderverse, and Venom, or whatever films Sony wants to make.
The breakup is a loss for fans, because all it means is no more MCU Spiderman, except for the part where Sony thinks that Venom's box office means that Sony is capable of making MCU-equivalent films now.
Rather than 50% of MCU-Spidey, and 100% of Sony-Spidey (since Disney asked for a share), Sony wants 100% of nothing, and 100% of Sony-Spidey. That's a loss for Sony.
The last time we saw Andrew Garfield's Spidey, Sony fucked things up by (among other things) trying to force a Sinister Six movie, because they had a massive case of obvious Avengers envy. Kevin Feige could deliver them 50% of a legit Avengers-style Sinister Six movie (although Disney would rightfully want 50%, if they're sharing 50% of the work and expense). But Sony would rather have 100% of whatever wet fart they decide to make by themselves.
And the guy who said "Spiderverse wasn't better than any MCU movie" didn't mean to say that Spiderverse was worse than the worst MCU movie (like Thor 2), he meant it wasn't "better than any MCU movie", as in, there are some MCU movies that are better than it (like Endgame).