I actually completely agree about the game not being challenging.

I don't want to keep bringing up XIII in every XV thread, but as XV's predecessor I really felt like that game was a decent challenge. You couldn't get too overleveled because the Crystarium only opened up stages as you progressed through the story. You could still farm and max out the Crystarium at whatever stage it is, but you don't become so overleveled to the point where you're just one-shotting everything.

The Paradigm System also brought a lot of options to the combat and made the game challenging. If you didn't paradigm shift in a lot of battles, you were going to get smashed. With XV I didn't have to use any tactics whatsoever. Just Gladio's AoE attack for multiple mobs, and melee attacks for every enemy in the game.