Sistar, 2NE1, SNSD, Wonder girls and even T-ara before the scandal would all have arguments to be #1.
I really have no idea why SNSD's digital power is so underrated. All their comebacks between Gee and Party were #1 hits. The record Sistar and Twice have with the 9 consecutive #1 songs would be SNSD's too if Gaon existed in 2009 (Gee, Genie, Oh!, RDR, Hoot, The boys, Dancing queen, IGAB, Mr mr and Party all reached #1 which would make 10, but they released Catch me if you can before Party which wasn't a proper comeback but people would have used it to leave it at 9 songs i guess). Their b sides also performed pretty good and even have some small hits among them.
It was always said that 2NE1 had better digitals but their way to promote was really different, with less comebacks but promoting more songs, they said all their songs were hits but they barely had proper b sides, it's like saying Cookie or Ditto are b sides now. With this I'm not saying SNSD did better but a direct comparison is really complicated. Sistar's situation was really similar to SNSD too. Finally Wonder girls' peak was 2007-2008 and it's even harder to compare them but they should definitely be included at the top tier.
Also just with the songs NJs have released in 6 months they'd probably make it into the list
1/2/3/4. SNSD/2NE1/Sistar/Wonder girls (+Davichi if we count them)
5. BP (+Bol4 when they were a duo if we count them)
6. T-ara (probably with the top group if they didn't have the scandal)
7. BEG (SUPER underrated)
8. Twice
9. New Jeans (Probably gonna rise)
10~. RV/MMM/AOA/Apink/Maybe you can add Ive already since they're probably going to go higher too.