I dont think is anyone is arguing that during the latter part of the 360s life and xbox one's, there first party was lacking, but thats a bit different than saying there game management sucked,
Might depend on what people specifically mean when talking about games management. It could just mean in terms of 1P studios, or also include IP not worked on specifically by 1P teams but still identified as Xbox brand-wise.
There are cases that can be argued in both that can hold true. On the studio front, they already had a scant handful of teams in the 360/XBO era and then reduced that even further by closing the likes of Lionhead. Other teams like Rare, arguably just did not live up to expectations for a lot of core fans whatsoever; not to say games like Viva Pinata and Sea of Thieves are bad. But for a studio that innovated platformers with DKC (and made the then-biggest 3D platformer ever with DK64), innovated kart racers with Diddy Kong Racing, and put out some of the best graphics in the industry with games like Banjo-Kazooie and Tooie, it's fair to say their scope in terms of being a leader of the pack fell off massively after their acquisition by Microsoft.
Maybe those older fans had/have unrealistic expectations; no one stays on top forever. But the fact a clear point of change can be marked pre-and-post Xbox acquisition is unfortunate. And going on, if it's more about certain games...
despite having less first parties they have still delivered some great games and now since there aquisitions I dont see any reasons why these devs cant continue to produce great games under the Xbox umbrella.
Yeah, they definitely delivered some great exclusives with the 360 and even XBO early on. In fact XBO had the better exclusives line-up for the first year or so between it and PS4, IMO. But after TitanFall, the quality arguably dipped because Quantum Break didn't quite hit as strongly as it should've. And Rise of the Tomb Raider didn't do as much for them as they thought it would; didn't help that Uncharted 4 pretty much crushed it on all fronts, and it's really starting with Bloodborne in 2015 that PS4 started pulling away in terms of platform-exclusives.
By 2018, it was unquestionably in PS4's favor by that point, some would probably say before that, maybe 2017 even, or late 2016. And the other issue for Xbox there was, they didn't do a lot for retention. Quantum Break should've had a sequel in 2020, all things considered, or a spiritual successor, that could've even been a Series launch title. Cuphead was a strong get but that IP is not really associated with Xbox despite coming out there first; Ori was another strong get but something happened between Moon and Xbox management and now apparently Moon doesn't want to work on another Ori going forward. It would've been neat to perhaps have gotten a Sunset Overdrive remake in time for Series launch, or a Ryse sequel, etc.
And I've said in the past that Bleeding Edge could've been delayed and timed as a cross-gen release between XBO and Xbox Series. It would've given the game a boost, probably helped boost GamePass subs earlier on, had more time for polish & tweaks, and more time for any needed marketing. Instead it's dead, and that's a more recent game. People are looking at what's happening with Halo Infinite right now and more than a few are probably concerned about other live-service games from Microsoft because of it. After all, if Halo is having these troubles, what hope is there for new IP or smaller brands they own? It's probably why people were worried when it seemed a new hire for PD is tied to live service games...
...and then shortly after that, the prior Game Director just leaves? Has the game shifted direction mid-development? Was it going to be something maybe more episodic, but non live-service based (like earliest reports mentioned), and now it's perhaps turned into a live-service GaaS? Is that potentially why the Game Director has departed?
Unfortunately with no official word on this stuff, we're just left to speculate.