Can mystic Gohan hold his own against Goku Super Saiyan Blue?
I think he is probably weaker, if you look closely at the fight when SSB Goku and Ultimate Gohan clash Goku seems to shrug off the two punches Gohan lands, but when a Goku lands one punch on Gohan he is visibly hurt and shaken. I would assume Ultimate form Gohan at this point is 60-70%  SSB Goku max since Goku wouldn't hold back after seeing his son like that.