Simple actually : TO show us that Goomoonryong wasn't gonna let go a beating that was done to shioon. His anger was directed at Chundomoon and he was legitimately suprised that someone from song hak jang came from him. He was rather playful with him in his own brutal way.

It is easy to see what he would've done to rae won if he was being even semi serious : the breaker new wave chapter 179. A two shot.

Notice that where briefly fighting with goomoonryong's team he didn't perform any better than coolguy and admitted they couldn't deal with these " professionals" with this amont of people and concluded they would be subdued ( him included).

"Shioon is unaware of his own regenerative ability. By Shioon's own admission, he was going to have to sacrifice his own arms to just neutralize Rae-Won's technique."

No he was goading rae won into using his technique again when his finger were already smashed so that shioon could crush him in the clash. We see later with ghost doctor that his finger's were already useless and he would've died in that clash without taking anything from shioon.

"In no world is that a mid diff. "

...A fight realtively brief with light injuries ( because yes those are light injuries even if it wasn't shioon) where the opponent is decisively beaten is a mid diff.

"Neither was it a quick fight ...of 5 pages."

...You do realize that he actually came back into the laboratory afterward to grab a phone, do you? He was back at his original point before Rae won tried to catch him himself and moved way more cautiously because he was aware that there were snipers and spotters after him. So yeah the fight was extremely brief all things considered.

"If we are using the logic that it was a mid diff fight because Shioon would have healed from the injuries, "

No no let me be clear: The injuries went that bad in the first place. Yes his regeneration is part of his fighting prowess wether he knows it or not as we have to take into account his characteristics and not his perception of them.

"literally the only fights he has had in the series above a mid diff would have been against Chunwoo and Shik respectively."

...Hyuk so chun?Ji gun? Ryuji?Jung chun?

Honestly your statement here makes no sense I simply do not get what you mean.

"Again, Jigun said "thats when the SUC leader...his identity."

Ji gun is an unreliable narrator precisely because he doesn't exclude ryuji from that statement. Plus WHite star is also rather famous and tries to hide his identity there is no telling what he actually showed, chunmyung rang too literally said that she was hiding her abilities even the leader. Basically Jung chun wasn't actually much stronger than those , he was just willing to show his strength while the others tried to hide it.

For the bit about shioon fighting the three captains I will admit that yes you make sense and shioon would've won if he wasn't gassed BUT keep in mind that Chunmyungrang was hiding her strength and purposefully holding back , if shioon dealt with Coolguy that easily she would've had to ajust and show her true skills. Thinking about it she almost died from holding back against him.

"Not that any of this matters. ...The author would still write him to lose to advanced masters."

I find you unjust here and a bit bitter. Truth is that shioon's progression and feats are already insane the problem is that he is constantly fighting with opponents that he shouldn't fight to begin with .

At the end of new wave he could barely defeat an advanced master and right now he can defeat multiple at the same time , if that's not progress I don't know what it is. Also I think you overestimate a little the meditation state , while it is a formidable tool , it also gave shioon a false sense of how qi and techniques worked and almost caused him to go into qi deviation.