Pretty sure there isn't, friend. At least from what I read and remember. But even by using logic, if Ruo Art was already standing at EX level, YG(Who still physically inferior to a average EX by Niki own words) wouldn't simply walk out of most part of Ruo's attacks. Or be so easily disregarded by current Wu Heir(Even though we can match probably near half the power of a MX all-out based on Chao's event)...
NOW, in a statement outside the book Niki indeed confirmed Ruo could hurt/kill a standing still MX using everything(Mostly artefacts. The statement is basically to show off how strong Ruo's gear truly is).
Besides that I agree with everything else, specially about the 116 check X 150 minimum cap comparison. Since the twins ultimate Art while fused was supposed to be strong enough to hurt a weak EX in old lore if I'm not mistaken(As the "bottom of X" was ~120-150).
Apologies, I mixed up Niki's statement with the game itself, still I think that since he's the author it's almost equivalent.
And while I do agree with your logic, my problem is that the logic is based on incosistent and constantly changing statements/scaling, and the fact that you said 'average EX' and not weak.
What is, and has been for a long time, my biggest problem, is the fact that the MCs stats are not being used at their full capacity. Niki checks for numbers that are 10-20+ points off from what people have been able to achieve, and considers anything beyond what he checks for impossible for some reason. Considering the last version I read, when Ruo sneak attacks the MC after the 3v3, if you don't do anything to defend against his slash - it cuts off your arm. Just flat out, without any checks or anything. And now considering the fact that just before that the MC potentially passed a 116 con check to defend against the Spear Twins combined Art, it means that Ruo has a casual Art that he flings at you which disregards your con being at potentially 116+.
Now this is ridicolous considering that at the time when it was released, the weak EX stat range was still 120-150 according to the lore/Niki. So if Niki just did a 116 con check, and then did not even bother to check your con for the Ruo attack, then his attack was at the barest logical minimum of 117 attack power relative to con if he considered 116 the max a player could achieve for some reason. And since we all understand that Niki would not set its power at such a random number without a check, it's pretty safe to say that it was at the time 120+ attack power relative to con. Meaning that at the time when the EX bottom cap was 120, Ruo busted out a casual 120+ attack.
Now that he raised the cap to 150 minimum for EX, it makes sense, but unfortunately it still means that Ruo's casual Art is at least 120 and probably beyond that, since I refuse to believe that Niki would check for 116 and not bother to check for 120 when it's so close to that. So in all likelyhood it's some number that Niki considers unreachable like 130+ and/or he just did that because he wanted to show off Ruo and no internal logic was applied.
Maybe that is why he changed the scaling again, because Ruo's attacks were technically too powerful now, I don't know. But still, before the rescale, Ruo's Art already did stand at an EX level.
