If I'm not mistaken, someone here has shown a screenshot of a comment by Nicky in the past. I won't look it up to be sure, but if memory serves it was something like "a Qi Sea genius might be able to defeat an weak/average Shangtian".
I don't know about Ruo being a Cultivator (I'll deny that reality until it unfortunately becomes fact), but it's not unrealistic for Qi Sea cultivator to defeat a Shangtian. This is simply the difference between the real thing and the copy. It may not be noticeable now, but the further you go, the clearer the difference becomes. I mean, Yichen Prime was so monstrous as a Shangtian that he was practically a category of his own, but even he was at most comparable to an "average Core Formation".