MS is relatively "inoffensive" as a publisher. It wouldn't be much of a problem at all if they became a full third party publisher while killing Xbox hardware in the process (and I mean actually exiting out - not just bleeding slowly to death - aka present condition). Much less of a headache for sure, although still a market player with a device preference - PC.
The problem is that they're a platform holder in the console space and as such can direct the industry in directions of their choosing policy wise that are detrimental to us as consumers and console enthusiasts. They're a cancer to consoles and they play that role well.
They're also of course the biggest PC stakeholder of this planet. Now naturally I much prefer Microsoft enclosed on the PC realm - way too many benefits. Also it's much easier for console manufacturers to tighten the noose on PC if required when there are less distractions on the console side of the equation. If Microsoft is powerless to directly and from the inside sabotage the console market that is a major win for every stakeholder in the console industry (including us). Unfortunately that is not the case, and it's not the case precisely because of this reason.
Make no mistake, Microsoft packing itself with two of the biggest publishers in this industry, specially publishers that catered to the ever critical WRPG/FPS genre that PC consumers like and is just as important to the console audiences is for a multitude of reasons. One of these reasons is that this makes sure PC as a gaming device is supported and covered, as well as partially shielded against a console manufacturer power play for the premium games industry. If those publishers were to stay independent, their support in a market split goes where the wind goes - that is, where there is market strength. This fact does not go unnoticed to MS, and they know that Japanese publishers will align with the dominant local. That is to say, Microsoft is giving the PC platform, the cushion the Nintendo platform has, or PlayStation has, and cementing it for PC. They're also doing that for Xbox, even if in a death spiral.
For illustration: there is literally no chance of Sony striking exclusive deals that leave out PC going forward for any ABK/Bethesda game/IP, even in a scenario where Microsoft kills Xbox and goes "third party". That is going to be eye opening for some, but all in due time.