Re: Thanos and Loki
I think Loki felt physical pain from The Other, and it was either immediate and in his head, or else he was remembering it and flinching from it. The Other definitely *****-slapped Loki in that scene off-camera, either physically or psionically, and Loki was still reeling from it.
As to The Other's relationship with Thanos in the MCU: it's very telling that he says things like "OUR Chitauri" and "WE," when he addresses Thanos, so he definitely considers himself an associate rather than an underling.
And as for kneeling before Thanos: Mephisto knelt before Thanos and was his *lackey* in the IG series. And Mephisto is, quite literally, Satan. If Satan bows before Thanos, I'm pretty sure *everybody* is fair game.
THE COTTON AVENGERS
...They move like slick cotton on oil.