He removes the gods ability to meddle in the world. That's it. He never makes her slave, he removes her ability to fuck with the world.
At no point does it ever state that he's angry that she did it. If there is please point it out to me, I'd like to know.
Goldmask saw how fickle and capricious the god were and realized that by removing their influence a lot of problems could be solved.
Ranni has her own agenda that would of eventually clashed with Marika, as it required it to kill all the gods, including her. Miquella on the other had is literally okay with stripping free will from people, as it states on the Bewitching Branch:
Tree branch blessed with an incantation of unalloyed gold.
Craftable item.
Pierce a foe, using FP to turn them into a temporary ally.
The Empyrean Miquella is loved by many people. Indeed, he has learned very well how to compel such affection.
The whole thing screams to me that there were several parties conspiring to kill Godwyn but each had their own private agenda and each thought they'd be the one to come out on top.
Goldmask looked at that said "..." and made it so Marika's, Miquella's, and Ranni's shitfuckery wouldn't dick over the Lands Between.