I do agree with you that Sony's 1st party studios are ahead of MS currently from a AAA perspective. Sony has 7 AAA capable studios now (Naughty Dog, Sucker Punch, Guerrilla, Santa Monica, Bend, Polyphony, and Insomniac), and most of those studios have now released critical and/or commercially successful games. However, that success comes at a cost, most of Sony's AAA studios are rather on the slow side, Horizon took 5 years to make and the sequel may take 5 years as well (if it gets delayed to Q1 2022, which is possible), Polyphony's GT games take anywhere from 4-6 years, Ghost of Tsushima took 6 years to make, TLOU 2 took 6 years. The slow release schedules mean that many of Sony's AAA 1st party studios only get 1 or 2 games out per generation. So, if you only like a few of those 7 studios like me, that is not alot of AAA exclusives to look forward to each generation from 1st party. Another problem with Sony's 1st party is that there is not alot of genre variety, most of them follow the same formula; open world, story-driven, action-adventure, it all starts to feel a bit samey after awhile.
As for 1st party A/AA development, I definitely think that MS has the edge here, on a personal level especially. MS now has many A/AA teams/studios, several of them with good track records. Rare's Everwild looks fantastic so far, Double Fine has multiple teams with a pretty good track record of releases (they've released at least 1 game per year since 2007, with several of them being critically and/or commercially successful). Compulsion's We Happy Few had alot of potential, but got compared against the AAA expectations people had for it, even though it was made by a AA team. State of Decay 2 was pretty good, though a bit of technical and graphical mess (being first party now means that Unreal masters like Coalition and Ninja Theory can assist them making the 3rd game look like a proper next-gen Unreal game). Ninja Theory's Project Mara has potential to be a great psychological horror game. World's Edge is shaping up to be a great PC/console RTS studio in the future. Obsidian's AA The Outer Worlds team is fantastic, and their single A Grounded has potential (played the demo the other day). By comparison, I'm not a big fan of Sony's A/AA 1st party offerings, never liked Little Big Planet, Pixelopus stuff isn't my cup of tea, Japan studio's Project Siren team puts out some good stuff, but the rest of their teams are kind of meh in my eyes.