You are seeing the here and now, not the then and there. Microsoft's acquisitions will have products in a few years and Sony will have a massive force to deal. Obsidian has made some really fan loved RPGs and that itself will bring people to Microsoft products. Ninja Theory could make a phenomenal hack and slash game as DMC Devil May Cry had the combat depth sorted. Playground Games will still make phenomenal arcade racing games. Turn 10 makes pretty good simulation racers. Microsoft already has first and third person shooters in their bag as far as exclusives are concerned. They could get the PR on their sides pretty quickly with these releases.
Most Sony studios do jack. London Studio makes nothing, Bend hasn't made a game since Golden Abyss and Days Gone is hardly blowing people's minds, Media Molecule hasn't madea successful game since LittleBigPlanet 2. Polyphony releases one game per gen and that too with a caveat. I adore GT Sport but it has got so many blatant flaws with regards to content that has been easily exploited by the competition and journalists who go by the PR and hype and people who haven't already played it don't see it as a good game. Sony needs more developers.
Platinum would be more successful on PlayStation.
During the Scalebound period of time, Platinum Games talked at great lengths about how they've wanted to make that game for a long time, and - more generally - how they've always wanted a series that they could cultivate and could call their own, that could be successful. In that respect, while you can talk about sales figures all you want, Nintendo is keeping a large portion of Platinum Games employed - and they're the ones that made Bayonetta into an icon, as well as owning the parts of Bayonetta 2 and 3, so I don't really see your point ... as it seems to be very flawed.
Granted Platinum Games most successful title was Nier Automata, but I believe the IP is owned by Square and the big head Yoko Taro isn't part of Platinum Games. Of course Bayonetta is owned by Sega, but Bayonetta has also only seen one developer throughout it's entire franchise ... it's not Bayonetta without Platinum, it could very easily be Nier and Drakengard without Platinum Games.
Not to mention i'm pretty sure that in addition to wanting to own their own IP, they also said they'd want it to be multiplatform. So Platinum staying multiplatform is best for now.
But yes, when you just completely forget all of those things .... Platinum would be more successful on Playstation 4 .... during the Wii U era. Let's see what happens when Bayonetta 3 comes out.