I also don't think Ruo will reach that level of power immediately after moving up to PH. Here let's deal with it mathematically:
In the scene where Ruo invades the training room and punches the MC, if the MC has 9k in constitution he doesn't take any damage, he just spits a little blood, you could argue that it wasn't all of Ruo's strength, but I doubt it was far from it. So we can assume that Ruo's stats are between 8k and 9k and that he stays in the top 10 with pure superior technique and Martial Arts, without using the transformation, this means that he has around 70% more power than he should have as a LH.
Under these circumstances, if he advanced and his strength exploded to its PH limit, he would have 17k in stats. However, I believe that at the moment of advancement his strength doesn't go directly to the limit, instead let's assume that it goes at most halfway (11k~12k). It's impressive, but still nothing unbeatable for MC and other of the more powerful PHs.
The problem is his transformation, we can't tell how much his stats increase, on the one hand he was able to hurt LC as a MH, on the other he wasn't able to defeat four PH as a LH. Since the incident with the rogues is more recent and since MC as a MH was also able to hurt LC, I'll consider that the transformation doesn't actually double Ruo's stats (I refuse to believe that a transformed Ruo with at least 16k is unable to deal with four rogues), instead it at least increases them by 60%.
Under these circumstances, right after advancing to PH, transformed Ruo would at most be able to show stats of 19.2k. Higher than any PH, but certainly not at the level of an EX, these guys should have at least 30k~40k.
