Ok. Reading through the whole thread and thinking further upon some posts (with thanks to atropos, redcurtain and MassiveKpopFan among others), I got curious.
So I did a 'quick & dirty' scan for all the groups and their songs. Basically an 'How did the best performing songs of each of the groups fare?'
What can I say? It was a slow Sunday.
It did show me some surprising discoveries. What I found:
BTS: ON (peak: #1, wk 20: #30), Dynamite (#1, wk20: #3), Life Goes On (#3, wk20: #33), Butter (#1, wk20: #10), Permission to Dance (#2, wk20: #18)
Hardly any surprises here, BTS songs peaked high and had good to great longevity, and BTS even had 1 of the few super hits. What surpised me most, because I hadn't been paying close attention to them, was how active BTS have been the past 2 years. They had a LOT of releases, probably the most of all the groups listed here.
Blackpink: How You Like That (#1, wk20: #19), Lovesick Girls (peak #2, wk20: #8)
In contrast, BP haven't been that active and didn't even have a comeback in 2021. But the few releases they did have in 2020 did great, with high peaks and very good longevity.
Aespa: Black Mamba (#49, wk20: #147), Next Level (peak #2, wk20: #4), Savage (#2, wk 18: #20)
Aespa started slow, but with Next Level they really hit it off. Even more: NL did phenomenally and NL and Savage seemed to perform as good as Blackpink's title releases.
Oh My Girl: Nonstop (peak #2, wk20: #20), Dolphin (#9, wk20: #10), Dun Dun Dance (#1, wk20: #23)
There's no doubt about it that Dolphin has proven to be a sleeper hit. That said, all OMG's songs of the past 2 years show good longevity which makes OMG 1 of the most consistent top groups.
Brave Girls: Rollin' (peak #1, wk20: #13 *), We Ride (#4, wk20: #24 *), Chi Mat Ba Ram (#3, wk20: #80)
For Rollin' and We Ride I used the moment of resurfacing as their 'first' week on Gaon to determine where they ranked 20 weeks after that. Where Rollin' and We Ride did great, CMBR had only ok longevity which seemed to suggest that the hype around BG seemed to lessen.
Red Velvet: Psycho (peak #2, wk20: #29), Queendom (#5, wk20: #69)
RV had the disadvantage of being incapacitated for a long time. Of their 2 latest releases, Psycho did impressively with a high peak and good longevity, while Queendom had a good peak and so far an ok longevity.
TWICE: More & More (peak: #4, wk20: #86), I Can't Stop Me (#8, wk20: #70), Alcohol-Free (#6, wk20: #63), Scientist (#32, wk 14: #143)
TWICE songs showed the same consistent pattern, of good peaks and ok longevity. Except their latest release, Scientist, that seemed to have been a bust. Somewhat of a surprise, I wasn't aware that Scientist did that badly.
STAYC: So Bad (peak: #159, wk20: -), ASAP (#9, wk20: #26), Stereotype (#27, wk20: #148)
STAYC is another slow starter. But then they hit it off with ASAP that turns out to be a little sleeper hit, to my surprise. They couldn't maintain it with Stereotype though, it didn't do that great (for a rookie group still ok I guess).
Mamamoo: Dingga (#7, wk20: #60), Aya (#37, wk20: -), Where Are We Now (#93, wk20: -), Mumumumuch (#102, wk20: -)
Mamamoo shook me the most, tbh. I knew that WAWN didn't chart well. But I wasn't aware that almost all their songs charted that badly that most of them didn't even make 20 weeks on Gaon's weekly chart. Only Dingga had ok longevity.
ITZY: Wannabe (peak: #6, wk20: #62), Mafia In The Morning (#10, wk20: #116), Loco (#26, wk20: #165)
ITZY's chart results seem to indicate a declining trend. Where Wannabe still had a good peak and ok longevity, their latest song Loco ended up doing a lot worse.
IVE: Eleven (peak: #3, wk 10: #5)
For fun's sake, I added IVE. So far Eleven performs very well on the charts. But yeah, probably still too early to draw any reliable conclusions.
Conclusions: what could be learnt from those results? When it comes to super hits, looks like there were a few. BTS' Dynamite and Aespa's Next Level turn out to be true super hits with phenomenal longevity, followed by BP's Lovesick Girls, sleeper hit Oh My Girl's Dolphin and BTS' Butter.
Aespa, surprisingly, performed as good as Blackpink's releases: Next Level has even better longevity than Lovesick Girls (in wk 38, the difference is even #16 for NL vs #29 for LSG), while Savage and HYLT have the same longevity so far. For Brave Girls, it remains to be seen if their next comeback will still benefit from their 2021 hype.
TWICE's chart performances aren't what they used to be. While most of their songs still had ok (but not good) longevity, their latest release Scientist really stumbled. STAYC, while being a rookie group, still had a good year in 2021. Their little sleeper hit ASAP had good longevity. Mamamoo as a contrast didn't chart well at all with most of their releases of the past 2 years.
Which made me think the following ranking's closer to the real situation as it stands:
1. BTS
2-3. Aespa / Blackpink
4. Oh My Girl
5. Brave Girls
6. Red Velvet
7. STAYC
8. TWICE
9. ITZY
(10. IVE?)
I've bookmarked this thread, will be intriguing to see how things will change as the year progresses, and what unexpected surprises will occur