Ironically, it was the leveling system which gave Square an idea to make an entirely new IP from it, which would then be known as SaGa. I wish the current Square Enix had this way of thinking when they tried to make something out of Final Fantasy XIII. It had great potential as a brand-new IP, and they messed that opportunity up.This problem was also on Final Fantasy I on the NES. I would say FFII's unpopularity stems from the dynamic and relatively weird no-level up stat growth system, not to mention wandering into the overworld and getting wrecked by a random battle levels above yours.
Still, I respect you for going through the original on the NES. I only read that review and some of its issues sound so frustrating.
Also, did I mention someone actually did a tool-assisted speedrun for the 8-bit version of II? Turns out the only consistent way to TAS this game is to abuse the 64-door hierarchy glitch in the nearest dungeon possible, which works in FF1, FF2, FF3, and FF4 due to shared coding. (NOTE: I actually tested the glitch with FF4 on real hardware, and it blew my mind).
If you did the glitch correctly, it turns out the game warps you to its ending. The inconsistent grinding based on random variables make it difficult to calculate an optimal strategy otherwise.