I think that when dalinar met odium first time, Odium was a shard whereas dalinar a mere human, he could not comprehend the infinite power and trying to understand would have broken his mind.
But later, Dalinar has kinda, ascended and that has put him in a more equal-ish measure to odium. Moreover, normally a shard’s majority power is lying in spiritual realm and it is not manifest. But, at that moment, dalinar had held a lot of that power manifesting it Directly in PR via creating the perpendicularity, so I think he saw odium’s manifestation in PR to be really small.