Having another studious is not bad either, you also need to remember, Sony attention now are divided into two platform, which are VR and Mobile devices (smartphones ). Also Sony capability on making first party ip in a year is limited to just one or two ip. With having another studios they will likely to produce more in a year. Of course they can just ask 3rd party studios to make exclusives games for them but having a studio that is inside your policy will be much better. And also like u said Japanese developer can be bought by money especially Microsoft , so . Having more is not a sin.
More like 3 -4 first party published games per year. And thats plenty from an exclusive standpoint any year. As opposed to MS one or two per year.
Sony doesn't need more studios. If they need to do anything its to get more out of their studios and partnerships.