He was beyond Odin, as we now know that Odin would've died in direct combat with Mangog, and Loki was well above Mangog.
For example, Odin vs Loki (of that particular story), Fenris, Mangog, Durok, etc = Odin gets trampled and killed.
Another thing, It could be argued that Mangog had all of his strength. It says on panel that Loki siphoned his magic. Mangog with all of his strength, couldn't budge RK Thor. But let's say that Loki did drain his strength. Loki with that strength couldn't stop RK Thor from casually plucking his head off as easily as plucking a grape off of a vine.
But let's attack RK Thor, right Abhi? This way we can avoid scrutinizing the Herald King's performance. Unless you're trying to lead us to believe that the boulder that drove the Herald King to his knees would also drive RK Thor to his knees, despite not being affected by any physical force that he ran into.