I think it would be wise for Sony to focus more on Japanese games period. They're become far too westernized this generation imo.
They need to buy some Japanese studios, so that they can have better sales in japan. I would recommend them to buy Level5, Platinum games, and Mistwalker. Japanese gamers are a bit xenophobic, so it does not matter if GOW is a 10/10, or if Uncharted 4 or Horizon are 9/10; they just don't care.
I dont think this will work. Sonys problem is not the lack of JPN studios. Its that their restructure of their current Japanese studios hasn't resulted in consistency of sales. They have 12 released PS4 games and the main movers have been BB, TLG and SOTC - 3 games in which they only ultimately co-developed.
SIE Japan is most lkely not going to release GoW/ Horizon esque games anytime soon, and they dont need to. They need more Gravity Daze/ Knack like games that are commercially successful and then to pump out games of a high quality on a consistent basis.
This is why buying other studios is not an effective means to bolster their Japan arm: they are still trying to get their JPN division to have the level of success that their US and EU divisions can achieve (stuff like Ratchet or Detroit). When they can do this, then expansion will make more sense. Likewise, Platinum doesnt want to be bought, Mistwalker is a waste of an investment having never released a PS games or is even currently in good shape. Lvl5 is just too big and the investment will go beyond owning the company but also will have to include restructuring.
On a side note, JPN gamers are not xenophobic. The current e-sports scene in JPN actually includes CoD, BF and R6. And Western sales have actually been better than in the past. The problem with Western IPs in JPN is that the market has been dominantly handheld for a very long time and Western devs rarely made good handheld games. So these IPs dont have any footing in JPN and never really will as long as JPN remains handheld-centric.