You're absolutely correct.
A lot of acquisitions do in fact have clauses that the staff in places of power are contracted for a certain number of years, so if Naughty Dog weren't a Sony Studio and Sony bought them, they would 100% have a clause that Druckmann, and a few of the other leads are contracted for 5 years or something like that. But developers come and go from companies all the time. Look at Rare, or Bioware, Rare has completely changed from where they once were, and Bioware is a shell of who they used to be.
There are some situations when you have a specific developer who has a vision that you would like to tie to your platform, like a Kojima, but that also is a risky play because if anything unfavorable happens he can just quit and then you have a studio called Kojima Productions with no Kojima.
Microsoft needed acquisitions because their 1st party has been lacking in quantity and quality of releases. They rectified the issue on paper, and now they need to deliver. Sony has high quality 1st party studios, and needs to grow the studios they already have to increase production times. Yes, sometimes more cooks in the kitchen make it more difficult, but I think they're ramping up the sizes of the teams because they have such solid leadership at a lot of their studios now.
