I really don't see how your arguments contribute to your point. Even if Activision Blizzard only had 4 franchises, an acquisition would still be much more drastic than an exclusivity deal. It is not the same as making deals for all franchises.
For an example, as much as Final Fantasy XVI is exclusive to PS5, the new Dragon Quest Monsters will be exclusive for the Switch. SquareEnix can choose what platforms to release what games for, including all of them if they want to.
And to be clear. No, Activision Blizzard doesn't only have 4 franchises, it has a whole portfolio of franchises, plus many studios under their umbrella. Even if the argument is that they aren't making games for some franchises, Microsoft could still hire them to make games for different franchises as an exclusive, without acquiring them.
Yes it would be good if Playstation had more competition from XBox, but I have absolutely no confidence that they will get there just by acquiring publishers. They already acquired Zenimax/Bethesda and Redfall turned out to be a disappointment. Same for Halo Infinite. I also remember how pretty much every Rare franchise died, they only have a single game going. Microsoft doesn't need to buy their way into becoming competitive, and there is no good that will come from doing that, it will only come at an expense of multiplatform games. What they need is to actually fund and make good games. Sony is making God of War and Last of Us with their own studios, they don't need to buy exclusivity for that. Same with Nintendo making Mario and Zelda. What is Microsoft making? What good would it be to let them have even more publishers and franchises?