If you fight every encounter in the game, you can probably 100% it too (in terms of completing all the quests). You might have to do some of them in a particular order, and grinding will definitely make some of them easier, but it's definitely not a game I would call grindy.

Though some people do consider a game to be grindy if running away from most random encounters and only fighting the bosses isn't enough to get to the end, lol