The characterization of this new Loki from the TV show trailer seems to me like it would be a believable development if it was Thor. Someone said TR turned Thor into Biff Tannen, and the snivelling attitude (”but I won’t do it again!!”) of this Loki is similar to how Biff turns out in the future where Marty’s dad punches him out (the car buffing scene - “that Biff, always trying to get away with something”). For Loki’s arc, it makes zero sense.
There would be two main believable paths for Loki to take at this point in his life as a former overachieving scapegoat child hell-bent on impressing his family, after the development of Avengers (and TDW, though I realize that’s in this character’s unrealized future) where he was in a spiteful don’t-care-about-anything-anymore phase:
1. Either he would become a helper: Someone very compassionate who very ardently tries to keep others from going through the same hells he did - all the while being very cranky because of his still aching trauma
2. Or he would continue the spiteful arc and be super honest about any hostile intentions he might have (and hide away the good intentions to keep from being mocked and belittled for them like before).
Those are the two believable arcs because those are the paths people with his past tend to go down. He can let it turn him bitter and hostile, or kind and caring, or most likely a strange mix of both.
But the backstabbing, unreliable guy who loves to hear the sound of his own voice and tries to grovel-smile and promise his way out of trouble even as he knows he’s in the wrong? That’s Schoolyard Bully Thor’s most likely next step (and even carries threads all the way back to ‘real’ Thor with the way he convinced his friends to go with him to Jotunheim, even though that Thor was still very innocent in comparison). People who act like that are usually either former Golden Children, or people with a poor sense of others’ emotional lives who are used to getting their way with no concern (or understanding) for what it does to others. Or both. And that’s TR Thor, not Loki.
It seems like the projection of Thor’s bad qualities onto Loki, which really should only be something the fictional character Thor does, is still rubbing off on the whole narrative. It’s getting old.