I don't think Thor's showings against Loki in the first Thor and Avengers movies accurately reflect how they compare in strength, as Thor essentially stated in Thor: The Dark World that he was holding back in those fights.
You should know that when we fought each other in the past, I did so with a glimmer of hope that my brother was still in there somewhere. That hope no longer exists to protect you. You betray me and I will kill you.
If you compare them by their wider records, Thor looks easily the stronger of the two. This is especially noticeable when you look at their respective showings against the Hulk in the first Avengers movie and Thor: Ragnarok. In the latter movie, Thor was on the receiving end of the same "puny god" attack that Loki took from the Hulk in the former movie, and endured it far better than his adoptive brother.
In another scene from Thor: Ragnarok, Thor forced Loki to stand between him and a returning Mjolnir, threatening to allow it to decapitate him if he didn't drop his Odin disguise. If Loki were Thor's equal in strength, he should've been able to break his grip there, considering that Thor was only using one hand.