The exhaustion from frenzy will really cramp your grappling for the rest of the day though, disadvantage on all ability checks isn't that big a deal for traditional melee warriors, but it's crippling for a grappler.
It's a very powerful build for one fight per day
True, although it can be ameliorated somewhat by using Greater Restoration at higher levels (probably not worth it, but it's an option). Another option is the dwarven Battlerager Barbarian - they get a bonus action attack when raging (only 1d4+str but still), advantage on athletics when raging, and they do 3 points of damage on a successful grapple check.