Brixton wrecks him in h2h. He can read and dodge his attacks all day . Plus Grey doesnt have anywhere near the feats of strength shown by Hobbs and Shaw to actually hurt him. On top of that, Brixton can one shot Grey with his " a jeep falling on my face is annoying so I'll just toss it off" strength.
And in the gunfight he needs a headshot or else Brixton is completely invulnerable.