Yeah, but what if I manage to convince you, huh? Oh, of course. That's why you don't wnat to, you're worried that I might succeed!
And I dunno. I don't think there was a lot of challenge in FF4 that couldn't be grinded past, except the bonus dungeons added to the GBA version. Same goes for FF5, really. The challenge in 5 is really just figuring out how the various skills interact, and the skill cap on that is relatively low. You should get to that point around halfway through the game on your first playthrough, and then it won't ever really get harder, except things that are countered by leveling.
FF4 is less complex (yes, even the non-easymode version) than FF5 again, so I'd say that has an even lower skill cap.