I've been (re)playing MS Saga: A New Dawn lately, a PS2 underrated gem of a JRPG.
It's probably the JRPG with the best progression and customization to date, as well as challenging turn-based combat.
It's not your regular "Buy new equipment on a new town and you're good to go" trope in JRPG. Each mobile suit has parts with its own stats that you can mix and match, and you can equip special parts on them. On top of that, there's also actual weapons loadout with the tetris grids like RE4. You can attach, remove, and swap weapons from any MS to the other as you wish, the only limit is each unit' weapons loadout size. Customizing and maximizing each unit might take a while but it's fun. You also have to pay attention to each character's (pilot) stats, traits, and skills to maximize each unit. I want to write a whole lot more about this game, but maybe later when I have the time and energy to do so.
The turn-based combat is so challenging even though you can swap between front and back members on the go like BoF and FFX. There are several weapon-based debuff like heat, acid, short-circuit and the likes that make combat even more interesting. Enemies, especially unique ones and bosses can easily wipe your party if you're not paying attention to their buffs and boost levels. Man, I'd do anything for them to remake and/or revive this gem in modern systems. There are so much more I'd love to write about this game, but maybe later when I have the time and energy to do so.