I think part of what makes this situation different than say Kratos in Mortal Kombat and Star Fox in Starlink is that both of those characters games were already exclusive to those consoles, so people without those consoles might not care as much on top of "well this makes sense", as well as Kratos not adding much content wise besides himself, though Fox was a bit more content if I remember.
While in terms of games Spiderman is only on sony stuff, Spiderman himself is a much more ubiquitous Marvel/Avengers/Comic Hero thing, he's much larger than Sony/Playstation. Fucking everyone loves/wants Spiderman. Not to mention that in this game in particular with how wildly different characters can play and feel and be part of the story/world, it's a massive change in experience between consoles. Spiderman is a huge character, and losing that on not Sony consoles can feel incredibly disappointing and like you're missing out on so much more than "Just a character".
Although I have multiple consoles, and if I get Avengers it will be on playstation (for more reasons than just Spiderman, but that is a big draw now), I personally think this is a dick move at least.
The 30 day exclusivity can also be potentially damaging in other ways, but this was mainly about Spiderman. (I have seen talk about how by the time other consoles get the added content, playstation will already be onto the next thing and thus you have a never ending cycle of being behind, which how much that matters vary from person to person but still)