The downgrade from MCU villain to MCU anti-hero

I do expect some degradation in skill between TWS and Bucky, but not something as drastic as how Spiderman completely, easily stomped him whereas Cap won against Spidey. That's such a huge disparity in skill that it's like a different person. Holding back shouldn't affect his overall speed and reflexes, just the lethatility of his blows. 

But then, at least Bucky has that excuse. Loki shouldn't have that excuse. This is the same Loki who had just finished trying to conquer Earth, so he should still fairly willing kill at this point. And yeah, the trucker in Walmart was just weird. Even if we consider that he was enhanced via magic, he was still using random store objects to smash and hurt Loki with... which doesn't make sense considering Loki can tank a grenade to the face.