There's no need to grind for the main scenario. Like none at all, you don't even gain stats past 20 apparently.
Even if you wanted to grind there's a few possible ways to do so, like the fight against the Ice King whose name I forget, each of the two fragments he summons give exp even after he cycles through all the elements. So you just have to get creative if you want to grind.
Personally i wouldn't mind having some bonus combat options like an arena or something, don't even need to give exp just have items drop or make vendors refresh their inventories occasionally so I can still keep using my endgame party in combat.
