Here is Loki's fight against Thor in the Avengers:
https://www.youtube.com/watch?v=9jqZQWuuaF8
At 0:40 you see Loki grab Thor by the head and smash his head on glass then proceed to throw him. This would not have been possible if Loki was much weaker than Thor. Even when Thor finally starts to completely pummel Loki, Loki takes multiple unanswered hits and yet still remains standing. Again, wouldn't be possible if they weren't within the same strength range.