LOKI LAFEUYSON IS A PROUD BOTTOM BITCH AND THAT IS CANON
Here’s my take: Loki is, at his core, a masochistic sub. He likes to be chained up and slapped. It satisfies his profound self-loathing. But he also, occasionally, enjoys taking the dom role just to see what it’s like. And if someone (*cough*Thor*cough*) needs to sub every once in a while in order to fully relax, Loki is willing to play along for their benefit.
The Avengers does not show Loki as an actual dom. It shows him playing a part, which should be obvious from the scenes that indicate he’s under severe pressure from Thanos. Loki is an actor; we’ve known that since the first Thor movie. He can play a tyrant when he needs to; he can even kind of enjoy it. But that’s not really who he is.
P.S. the dom/sub contrast is separable from the top/bottom contrast. @illwynd’s powerful Thor/Loki fic I Remember a Shadow portrays Thor as a dominant bottom and Loki as a submissive top. It’s the sub aspect that’s core to Loki’s character, not the bottom aspect.
Loki is the Philosopher King 