I'll admit that I haven't heard that many live vocal performances from GFriend's subvocalists. Still, I think that it's Red Velvet of these two groups, even if I had heard more GFriend's vocal performances. For reasons explained more below.
I kinda agree and disagree.
To be frank, I haven't heard GFriend and RV vocals and subvocalists be praised that abundantly and excessively to the point that they can be seen as 'overrated'. In fact, I think it's the more opposite and in RV's case it's almost to the extent as how SNSD and Super Junior were masssively underrated and put away as 'talentless visuals' and even ridiculed when objective vocal analysts mentioned they wanted to give a Super Junior vocal analysis a shot ('why would you even want to analyse the mediocre vocals of that zero talent group?') on sites like this one.
For RV too, I can't count the many times in previous years that RV vocals and vocalists and their vocal talents were dismissed and trivialized, on this site too, and ignored when talking about top tier vocal girl groups of 3rd gen ('oh, it's just Wendy that's strong, the rest are forgettable'). Completely forgetting that Red Velvet are one of the few girl groups that sound truly (and effortlessly) amazing when singing live, and that even the RV subvocalists sound good live and know how to harmonize impressively.
Which, honestly, should come as no surprise that RV as a whole are a top vocal group of their gen: SM has always had an intense focus on delivering strong vocalists and have their entire groups sound great while singing, which is partly due to SM's impressive vocal coaches and vocal coaching they invest in. SNSD, DBSK, The Grace, SHINee, EXO... RV is just 1 SM group in a lineup of strong vocal groups.
Respectfully disagree here.
You might hate or dislike SNSD or SNSD members however you like and not like how SNSD's vocals sound - what vocal color or tone you like is after all a matter of personal, subjective preference. But it's a matter of fact that SNSD is a top vocal girl group and that their entire vocal line is easily as good as and better than the majority of main vocalists of 2nd gen-4th gen girl groups, vocal technique-wise. And even their subvocalists can still sing and harmonize well live.
Like said, just like every company of the Big 4 had their particular talents and strengths they focused on for their groups, vocals and harmonizing were the traits that SM focused on when it comes to their groups, especially in earlier gens.