Golovkin knocked out Simon in one round. The same dude that went the distance with prime Arthur Abraham when he was considered p4p hardest puncher in the game. Obviously Donaire has fought far better opponents but that Simon KO speaks a lot. He was never down in his career. Golovkin is fighting guys that weigh more than him on fight night too. Donaire had been fighting smaller guys for most of his fights.
Donaire KOed guys like darchinyan, arce and montiel and those knockouts were all highlight KOs. These guys have proven elite chin, arce may have been stopped before but he got stop in the late rounds and due to accumulation of punches. Darchinyan, montiel, nishioka, donaire is the only one to knock them out and these are world class fighters
Donaire has proven power against top opposition, Golovkin has yet to prove it, but I believe he will when the opportunity arises.
I'd argue that GGG punches heavier, as opposed to Donaire who punches much sharper. Different kinds of power.
Even if ND reach WW, haters will claim Nonito is always fighting midgets. Disregarding the fact that their heroes Moralles, Margarito, JCC Jr. and loads of Latinos have always been midget killers.