He's unfairly matched against people who are above his weightclass or are super human.
glass joe[base] deals 10 dmg in all of his moves thus tkoing little mac in 10 hits, thus his power is actually above an average boxer.
little mac can launch and stagger people above his heigh class and glass joe can decently tank some of the punches unless he gets surprised during viva la
glass joe[td] can deal roughly 15 dmg in most of their moves except for his right uppercut which deals 19 dmg almost mr. sandman's jab[21 dmg] whose punches can break cement and bricks.
glass joe from punch out isn't weak.
i rest my case