I'd say there is a general vibe to JRPGs that you can't really get at by just describing the combat system.

It’s easy to imagine someone who like Final Fantasy may like a game like LISA. But harder to suggest someone who like Final Fantasy will like Kingdom Hearts

If anything, I'd say the opposite. Even setting aside the developer and series overlap, I would expect a Final Fantasy fan to be much more receptive to Kingdom Hearts than to LISA. While classic Final Fantasy may be closer to LISA mechanically, FF and KH are working in a related tradition that LISA is a bit farther from. There's connective tissue between JRPGs that go beyond their mechanics, and this is part of why FF as a series has gone between so many radically different systems while still feeling united in some way. JRPG may not be a perfect term, but it carries historical reality, not just bland mechanical descriptions. If you look at music for example, genre titles are just as often describing the scene something came up in (or is emulating) as they are describing the sound itself. If genres are to give us helpful groupings of games that are related to one another, just describing their bare mechanics isn't enough on its own.