He really seemed to give too much away in this fight. Put the first two rounds into doubt for no reason, went headhunting in a few rounds that Jacobs pulled out, didn't throw enough in general, no bodywork.
I think GGG did enough in the first rounds to win the fight. He won 4 of the first 5 and clearly won the 9th iirc. It would be extremely harsh on to give every round to Jacobs. For me the range of possible desitions were from 115 to 113 to GGG. If Jacobs would have won it would have not been a robbery or anything but I would have thought GGG was unlucky to lose.
One final thought, both fighters were at their best when they threw short, straight shots. They weren't as big of bombs as when they wind up, but both fighters really struggled when throwing bombs. For example, Jacobs threw way too many open handed punches, while Golovkin fell into the habit of launching bombs at the head. Hindsight is advantageous, but it really felt during the fight that Golovkin needed to just work the jab and work the shorter power shots like that uppercut that disappeared as quickly as it came.
Jacobs doesn't look so natural out of the southpaw. Many fighters don't seem to look so good when they switch to my non expert eyes.
If they fought a rematch GGG probably wins more convincingly because he'd game plan for this. Jacobs wasn't clean from southpaw, but it's what kept the fight as close as it was. Mainly it seemed to neutralize the jab which Jacobs was eating in the first three rounds.