I generally find jrpg combat to seem simplistic, but this could be because I only played a few hours.
JRPG combat does tend to ease you into things, and aside from that, low difficulty in many can render complexity meaningless even when it does show up.
Avoid Final Fantasy games, only a handful have decent complexity and they all lack the challenge to make use of it.
I'll second the recommendation of SMT 3; it'll ramp up quickly and there's some challenge as long as you're not reading a guide to do some broken shit and it's about as close to a traditional jrpg as you can get that fills that niche. It's fairly mature in tone as well if that's a factor. Don't play on hard, it's a dick puncher that will cause a lot of resets from RNG.
Breath of Fire 3 doesn't get quite as crazy, but if you were considering Dragon Quest games for the atmosphere, I'd strongly recommend BoF 3; it's very charming and has much better gameplay, though it is a very slow start before you get into masters and dragon genes and such. Probably the only JRPG I know of that successfully walks the line between colourful kid friendly stuff and mature themes. It's also very, very pretty.
Those are probably the only really traditional jrpgs I'd recommend to someone that's bounced off the genre before due to simplicity, but I've got a lot more I'd recommend that aren't quite traditional (or quite japanese) but are excellent games that get lumped in that category:
Monster Sanctuary has basically no story to speak of, but the combat is excellent- lots of crunch, lots of difficulty by the endgame. Fairly quick to start too. Play on hard.
FFT is great but it's definitely a tactics hybrid as opposed to a traditional jrpg. Troubleshooter is arguably a better version of that with more complexity, made by korean devs. I'd throw in Labyrinth of Touhou 2 as well; it's basically a wizardry dungeon blobber without the first person perspective though. Great combat however, rather unique 12 man party with 4 in combat at a time system.
If you're into open world stuff, SaGa Frontier and Romancing SaGa games are traditional jrpgs that basically just drop you into the world right away and let you find quests, dungeons, and places to get killed. Crystal Project is an excellent game made by a single dev that works jrpg style combat and a complex set of classes into an open world 3D platformer. Note for all of these I mean open world in the sense that the gameplay is completely nonlinear and you can stumble your way into areas with very powerful enemies and loot pretty much right away, and there's little to no handholding telling you where to go. They're not a series of big empty fields you spend hours walking across in search of something to do.
