i think its not necessarily a physical lack of power, its that he throws short punches in combinations to land faster
his hand speed and chin are what carry him. hes a brawler who blocks strikes with his face, but he has good power and throws punches in fast succession, so he overwhelms people. he forces them to deal with 8734984723978 punches to stifle their own offense
if he doesnt have his iron chin, he wouldve been ko'd by the strikes he took from jones, shogun, jan and maybe manuwa
he rarely blocks punches with his arms, and just keeps punching instead. thats dangerous against strikers like rumble who have the power to knock him out, but low power volume strikers like jones have no way to strike him off and keep him at bay. jones landed a ton of headkicks but gus just kept punching through them
look how his instinct is to just keep punching while taking shots that would ko most fighters. he doesnt even try to block when hes getting hit
when he finished manuwa, it was the same thing, he rushed in with 0 defense but kept punching with so much volume that manuwa got overwhelmed didnt fire anything back. gus even led with a rear hand uppercut, with his left hand down by his waist, absolutely 0 defense.
i think thats why his 5 round decisions are such wars. its very exciting to watch him wade through a firestorm to land his own combinations