Doesn't hurt to have more if they can afford to maintain them.
I do think its rather odd you say they have too much support when this year they only showcased 4 major AAA games at E3 2018 and basically dropped out of E3 2019 due to nothing new to show.. or so the rumours say.
Also keep in mind the gaming industry isnt all for Japanese games. Not everyone (like myself) are into anime styled games. I see alot of that on Steam and i ignore them, just my personal preference.
Also games like SFV was a sellout to Sony but keep inmind Xbox has there very own inhouse fighting game. SFV was basically Sonys anwser to Killer Instinct due to a lack of a inhouse fighting game from themselves.
Should Sony buy out more studios? I say yes because of VR and the lack of games they showed this year. Games are taking longer to make, 3 to 4 years is becoming quite common so having some AA games doesnt hurt to fill the gaps.
Next gen if Xbox and Switch eat up alot of the 3rd party support PS is relying on than thats where they need games on a regular to keep there audience interested. I say the same thing with Steam because Valve rarely makes games and other Digital stores are starting to offer the same amount of support to compete.