That is such a terrible take.
When I made that comment I was considering those studios on their own merits. Neither is a proven AAA studio.
Ninja Theory have been, up until now, an independent studio They've made some games with decent production values and had some level of critical acclaim, and the only time they've been near AAA territory was with someone else's ip (DmC). I think they will become a very capable studio, but they're just not there yet.
Its a similar story with Obsidian. They've done some good work, especially last gen with Bethesda ip, but they're not a polished AAA studio. They've succeeded in the last 8 or so years (since being fucked over by Bethesda) by producing reasonably selling games on a modest budget. Pillars of Eternity was a kickstarter project ffs.
Xbox Games Studios have definitely acquired a couple of very high potential studios here, and with investment over the generation the results could be exceptional. But they're not there yet.
I didn't make a comparison to Sony studios, but you did and in doing so you're just making yourself look a bit silly. SIE have 13 studios, so by your reckoning 95% i.e. 12 of 13 are mid tier. That's just a terrible hot take, there's at least 7 or 8 top tier studios there, 5 of them have produced games that have sold over 8 million this gen.