What about Disgaea 5, it's on PS catalogue. It looks more somber in tone. You tried it?

I also really enjoyed Ni Nu Kuni, both of them.

This is the Answer, Revenant Kingdom, that Chat GPT4o gave me when I asked about games similar to Tales of Arise. 

Live A Live, if you want a pretty nice varied experience. It does a lot of things you don't typically see in RPGs.

Anywoo, I'm surprised you bounced off Star Ocean Second Story ... Otherwise, Etrian Odyssey III or Labyrinth of Galeria if you want to look a bit into dungeon crawlers (lots of good Indies too on that front).
SMT V Vengeance is a pretty good one coming up too.

The best JRPG of all time is Chrono Trigger in my opinion, it's not on Switch or Ps4 but on Steam if you have that. Star Ocean 1 and 2, Sea of Stars (jrpg like), Super Mario RPG and Paper Mario Thousand Year Door on Switch, Bug Fables if you like Paper Mario. Not rpg, but if you like old school Zelda games both Blossom Tales game on the Switch are fun. Lost Sphear is made by the same company that did I am Setsuna. Grandia 1/2 HD remake, the soon to be released Dragon Quest 3 2D-HD remake. Not sure when the Suikoden 1+2 remaster is coming out, but fantastic games. Xenoblade games on the Switch. Tales of Symphonia is also one of my favorite jrpg of all time. Edit I didn't read the underrated part, but I stand by these.

I think it is the 2nd best Disgaea. Just avoid 6 for a bit until you try the better games.

Unfortunately I havent played D5 yet.

I've only played Disgaea 1 on PS2 back in 2007 or so and PC about 3 years ago or so alongside Disgaea 2 on PSP back in the late 2000s.

Planning to play Disgaea 2 on PC soon and I do have Disgaea 3, 4 and D2 on PS3 - also have Disgaea 4 and 5 on PC, Switch and PS5.

6 I'll get on PC first sometime in the future and 7 as well.

What even is 13 sentinals Aegis Rim? It's not a JRPG. More like a Graphic novel that's also a puzzle with a strategic side game. There is no genre for this, right? This is totally unique.... cause it's awesome.

That's a lot of gaming to get through based on How long to beat stats. Like an near impossible amount. Disgaea 5 is 88 hours alone with mixed style which is usually the most accurate and 222 hours for 100% completion. 

SRPG