Even this seems to vary by title though. For example, the follow-up to Digimon Story: Cyber Sleuth (a Vita game with a later PS4 port) isn't coming to Switch, and other Vita/PS4 titles still seem to be following this pattern (The Lost Child, Tokyo Xanadu, Danganronpa, Legend of Heroes, etc.)
A few exceptions like Fate, Dragon Quest, and Puyo Puyo Tetris stand out, but Switch still has a ways to go before it can even brag about the sort of 3rd party support the Vita had. On the inside front though, I'd say it's more or less already there.
I don't think Switch will ever get all the Japanese support it "should" get, i.e. all console support that depends on (or could really use and get) more domestic sales than it can achieve on PS4.
As for small PS ecosystem JRPG companies:
I doubt we see Falcom on Switch, although they have expressed interest (in having someone else bring their stuff over, presumably). NIS and Gust seem to be getting on board.
As for core 3DS partners:
It is picking up good support from SE. Dragon Quest looked to be shifting to PS4/Vita from 3DS for a couple years now, and that has shifted over PS4/Switch going forward. Tokyo RPG factory is now on Switch. Project Octopath Trailer is going to continue the Bravely Default line of support on Switch. The fact that they are even suggesting they may want FFXV in some form on Switch is suggestive of them looking into even the tightest fit and sort of SE support that seems least likely.
Atlus is at least continuing SMT on Switch. We'll see what happens with Etrian Odyssey. We'll also see if Nintendo picks up support in terms of a hypothetical P5P or not. But we do know Atlus will be on Switch.
I think we can also believe that SEGA will continue to put out at least Sonic on Nintendo systems.
Capcom is obviously disappointing. They seem to have thrown their lot in with PS4 being more successful in Japan and/or Nintendo being unable to succeed the 3DS successfully. It does seem that they are transitioning Switch into their future plans, but they are clearly slower at doing so than, say, Dragon Quest, which also was going PS4 over 3DS/3DS successor at first. We'll see if there is a new portable Monster Hunter in 2019+. I'd imagine the second team is probably working on such.
Level 5 is another traditional partner that is a bit of a question mark right now. They are in-between cash cow franchises and sluggish in their mobile endeavors.
Namco and Koei Tecmo are both present with their Nintendo games. We'll have to see how much Switch figures in their releases beyond that.