I think the ABK acquisition needs to really be looked into perhaps even beyond what the FTC are currently grilling MS on, because another component at play here are game technologies for engines, frameworks and middleware that Microsoft could potentially be looking to own even more of, to control and leverage distribution and ownership of those technologies among game devs and pubs to net specific benefits for their gaming products in ways that competitors may not.
There's a glimpse of this already with the Sega x Azure strategic partnership, and the correlative benefits Game Pass has seen in getting ports of many Sega & Atlus games to that service, in many cases Day 1. I am pretty certain those benefits have come as a direct result of the Azure partnership Sega has. There are other things to keep in mind as well, such as Azure Playfab, and Havok (the latter MS acquired in 2015 from Intel).
I am not saying these things in isolation are bad, and Sony has similar technology ownerships that are licensed out to many different gaming companies, even Microsoft in a few cases. The problem is that Microsoft possess the ability to buy out the market in these regards due to a combination of the sheer amount of money they have alongside their expressed intents to dominate the industry.
And I keep stressing as well, the 2019 email does not help their case here whatsoever: one of the other means acquiring 3P publishers could be used to "put PlayStation out of business" is through buying ownership of any proprietary technologies those 3P have, and controlling the licensing and distribution of those technologies to direct competitors like Sony in ways that could be unfairly (to the licensee) amplified by ownership and control of related assets relating to the same acquired 3P entity, that a direct competitor may also rely on.
Again, it's just like the idea of M&A acquisitions themselves: it's not inherently a bad thing. But when dealing with a company of Microsoft's size, with its history of anticompetitive actions, & expressed intent to put direct competitors out of business combined with certain false narratives and half-truths they have already spoken about WRT direct competitors to influence public optics and even legal decisions (not to mention expressed intent to make further acquisitions in gaming beyond ABK), it creates a total picture that basically screams "block this deal.". Or at least a block without structural remedies applied.
...and that's even before taking into account what precedent this will set for other big tech companies looking to further consolidate the industry, themselves. At some point you likely won't have a 3P market aside from indie startups, and that's not a 3P market that can sustain itself seriously for any decent period of time.