We realistically can't say SCE didn't try. SCEJ in particular pushed Monster Hunter more than any of their own IPs.
I've said this before, but they made a specific PSP revision just for Monster Hunter. It wasn't just a bundle. It was new model that featured an improved analog nub, and built in back grips to go with the extended power battery. This PSP model would never see a non-MH branded release. They also made MHP3rd the star of the PSP Remaster program, and the first PSP game to be shown playable on Vita was Monster Hunter.
That said, it's clear that SCE is more interested in developing their own IPs than helping third parties as a whole right now. I don't blame them given how many times they've been burned by helping a third party only to see said third party release their wares on competing hardware. They're probably rationalizing it as a better investment to build their own brands than to spend that same money on securing some form of exclusive support from the third parties. That's a fine strategy for the console space because games have become so expensive to the point where third parties are rarely going to make an exclusive game so SCE's guaranteed support, even if it's not exclusive. However, in the handheld realm, games are cheap enough to make where being exclusive is justifiable for most third party games.
It's already too late for that. SCE should've been buying Japanese studios before Vita launched. As for your suggestions, imageepoch is poop and SCE may have screwed the pooch with From. Platinum is too close to Nintendo for SCE to buy. Buying Tri-Ace is pointless as SCE would only get the studio's name, and the employees. They own none of the IPs they've worked on, and given the performance of their non-SE published work their name means little.
In an ideal world they should've co-purchased Shift with Namco Bandai (ala Cellius) and make God Eater their face instead of making Soul Sacrifice. Heck, Shift worked with SCE in the past too ...
I'm not sure what they can do. Gran Turismo is fading in Japanese viability, and Hot Shots Golf isn't a system seller, but rather a game that is bought alongside systems. Those are their biggest IPs. SCE as a whole has struggled to make blockbuster hits, and they really can't rely on third parties anymore as Vita has shown. While PS4 won't suffer the same way Vita is, because of guaranteed support from Japanese IPs that have global appeal ala Metal Gear, Resident Evil, and Final Fantasy they've lost the likes of Monster Hunter, and Dragon Quest.
Seeing the likes of
Okamoto, and
Sakaguchi work on games that barely even qualify as such isn't something I like seeing.
