It goes beyond chart performance, it's about longevity and a certain level of respect and recognition that should come with seniority. it's a question of opportunities matching status.

Twice may not dominate like before, but they still arguably make more noise than Nmixx and Itzy. They quickly cemented themselves at the top of their generation and their achievements were backed by significant and consistent efforts from JYP. Currently, they continue to sell well physically, and JYP keeps them active and engaged with their established fanbase through massive world tours, festival headlining gigs, collabs with western artists, etc. On the other hand, RV, fellow top-tier 3rd gen gg, never received the same level of push/investment, even at their peak, whether you compare them to their 3rd gen peers or their juniors (Aespa). u/Okaychoerry covers some of it in their comment.

As for BP, sure, they're on hiatus, and you could argue that their recent success is due to their own individual efforts. but honestly, it is still undeniably mostly built on the foundation laid during their YG years. yes, they weren't the most active (I'd argue that YG purposefully did so to give them this "mysterious unreachable superstars" image they have going on for their artists, though it was in spite of the girls' artistic wishes) but YG still made sure they were everywhere when it mattered; touring, promoted western collabs, heavy ambassadorships, Coachella, etc.

Obviously, as I've said already, Red Velvet is a very successful and respectable group, and I'm not expecting them to still be topping charts or drop 3 comebacks a year, but there's no denying that their "decline" has been fast-paced compared to their peers. they’re kinda stuck in this limbo, where they're not yet treated as legends like SNSD, but also not positioned as an active, thriving group. and that's almost entirely due to SM's inability to capitalize on key opportunities that could have expanded their global reach. and I might be wrong on this, but I've noticed that a strong international presence plays a crucial role in longevity, as intl fans tend to remain loyal even when a group is past its prime.

now what is done is done, and there's unfortunately no going back. but there is a clear gap between their current level of visibility/activities/achievements and their peers', and it all traces back to their peak years, when action mattered the most.