So much nonsense nowadays regardless this.
You have groups that have sold more than SNSD for example and are nowhere near their impact. Digitals, touring, general public reception, etc are criterias for top groups.
If we do the ranking just base on total sales it will be like this:
4. TWICE
6. Seo Taji and Boys
7. H.O.T
8. SUPER JUNIOR
9. SNSD
10. god
And we all know that ranking is off if we use it to determinate top groups.