Think of it though. Venom made $800m. Marvel's last few movies have been $1b.
If Sony lets Marvel pay for 25% of production costs but only take home 75% of the box office, assuming Marvel gets them a few more $1b+ movies, they'll be out in front *and* get to claim more $1b box office hits, helping their company value and stock prices.
And none of these articles seem to cover home video/streaming profits. As much as I was okay with the Venom movie, I likely won't see it again. I've seen the MCU movies 2+ times each (granted, anything that is just a flat two times was only in theaters - although, ironically, I've only seen FFH once) and am eyeing that box set. If Sony gets Marvel to do the legwork on their Spiderverse, I really see no downside for them.
Honestly, I don't see why Marvel pursued Spider-Man so fiercely. I'm glad it's in the MCU, but honestly, I think the entire MCU would have developed Civil War and beyond without him just fine*. Let Sony Pictures continue to struggle to understand the formula and eventually sell the rights back to Disney or be bought by Apple and the rights revert back. I can only guess Marvel didn't want Sony to taint the Spider-Man franchise to Fant4stic levels of bad before either of those happened.
*Assuming there was never an MCU Spider-Man. Once he was there, there's no going back.