There are specific benefits to having a large, independent 3P market and consolidation by platform holders and tech companies looking to become platform holders weakens those benefits, if not gets rid of them completely. 3P being acquired by investment groups pose their own issues depending on the specific investment firm, but not the same problems as the other examples given.
When there is a strong independent 3P market, there is generally more incentive for them to bring their AAA releases to as many platforms as possible. Creative decisions and funding solutions are not tied to the larger corporate culture and financing well of a single corporate owner. The games run less of a risk of becoming locked behind any one specific platform or ecosystem, because since most 3P publishers want to maximize profits, they have more of a real incentive to provide content to as many platforms and ecosystems as they realistically can.
A strong independent 3P market also means more inherent competition among the companies to make offerings that stand out in the market, and due to that,, sometimes the impetus to even make certain types of games in the first place. How likely do you think we would have gotten Fortnite if Microsoft owned Epic? Or Apex Legends if Microsoft had acquired Respawn around the time of TitanFall?
A healthy independent 3P market also means case-by-case chances for platform holders to partner with specific 3P developers on games that may not have been made otherwise, but those partnerships not locking the 3P developer out from doing other projects for other platforms. This is what we got with both Demon's Souls and Bloodborne, for example. If Sony had acquired From Software back in 2009 or 2015, chances are you would have never gotten Elden Ring for Xbox. In fact there's a chance you may not have gotten Elden Ring at all, but rather a Bloodborne 2. Instead, we're in reality where we have Elden Ring, and Sony can still collaborate with From Software on a Bloodborne 2.
As you can see, I don't exactly support the idea of rampant big 3P dev/pub acquisitions, regardless of who is doing it. While I think Sony WILL have to respond to MS acquiring ABK with a publisher acquisition of their own, I choose to refrain on deep-diving with speculation on that. However, I do feel there are levels to this. Just looking at how the respective companies have shown (or not shown) the ability to cultivate and grow their acquired talent to do bigger & better things, I would personally feel more comfortable with a Sony 3P acquisition than a Microsoft one, because cheapness of availability or having access to my games on 100 devices that I know 99% of them won't see the time of day in terms of serious gaming time, aren't at the top of my priority list as a gamer.
But maybe for you it's different. Maybe those things are your main concerns. Cool. I can't agree with that. But I can acknowledge that is your opinion.