Yes bp twice and rv are legendary but all the other ggs kind of faded in comparison even if they're good or popular at the time like clc, oh my girl, mamamoo, wjsn, momoland, i.o.i, pristin and gfriend
Meanwhile 2nd gen not only had snsd and 2ne1 but t-ara, kara, sistar, aoa, f(x), girl's day, apink, wonder girls, miss a, just to name a few.
4th gen had many great ggs from start like itzy, loona, everglow, g idle, I*zone, and later stayc, aespa, Ive, nmixx, lsf, newjeans, kep1er and even the smaller groups are really nice even though they got overshadowed like woo!ah!. even fifty fifty already ended but made history by making one of the bigger international hits
I think this 5th gen talk is bs but even if it's really 5th gen they're also killing it not only the most popular names like illit that debuted breaking all sorts of records and babymonster that were super hyped and are skilled af, but also groups like young posse, rescene, unis, kiss of life and geenius that barely debuted and already show big potential with great music, concept, skills, styling, mv (well at very least one of these)
so yeah when you put it in perspective I think 3rd gen really was the weakest even though they had memorable stuff