Golovkin is the far superior boxer, better footwork, power, timing, angles, jab, better athlete, amateur's phenom, and yes even better defense, but you have to know what you're looking at to get it... Also stats don't lie, Golovkin is between the top-2/3 in the world at "hit and not getting hit"...
But maybe age can play a factor, as well as a long career, still i wouldn't look too much into Brook and Jacobs bouts, different opponents, mindsets and strategies... Then we have the usual suspects as judges and ref, the Vegas mafia that's going to favor the A-side Canelo, Kenny Bayless as referee, and two of three notorious corrupt judges, Dave Moretti and Adelaide Byrd...
Golovkin has to stop Canelo, or the decision goes to the mexican no matter what probably, or maybe it's a fixed sparring session to get lucrative future rematches, wich is a possibility also...
The weigh-in is also extremely early, giving Canelo more time to rehydrate and survive with added weight, exactly the same anomaly that happened with Jacobs in March... So Golovkin has everything stacked against him...