Tricky question. Of course it is very difficult to compare boy groups and girl groups. However, everyone seem to agree about Seventeen (and sometimes NCT) being above these two girl groups. And I tend to respectfully disagree.
Seventeen is a wall in terms of physical sales and tour numbers, sure.
However, both Red Velvet and Mamamoo are a wall too in terms of digital performance and public recognition. Having also two members with their faces all over South Korea.
Seventeen and NCT have huge fanbases but they can't match with the public recognition of RV and Mamamoo and they're pretty much mid tier groups outside their own fanbases. Even in Japan, where Seventeen is supposed to be big, their streaming numbers are not really impresive.
So which one is the bigger act? Are sales really that much important compared to digitals/CF deals and public recognition?