The size is less my worry than that his foreskin looks tight, like, does it actually slide down? Cocks that aren't circumcized should have their forskin withdraw when erect, which he is so, is he one of those cases where the foreskin is so tight he CANNOT pull it down??
This would explain the cuckery more than the size, if his foreskin physically couldn't withdraw / sex was unbelievably painful on his dick because friction, from his dick basically being trapped in a too tight foreskin which cannot pull back for normal function
Theres actually a word for this, Phimosis, does he have this medical condition? I haven't exactly examined tons of dicks but the ones I've seen always at least PARTIALLY retract when hard.