with bts being an obvious example, it feels like most 3rd gen groups are doing suprisingly well over 5, sometimes even 7 years into their career.
despite their digital downfall twice still outsell themselves, their concerts in the us sold exceptionally well, if jyp manages them well (and most, if not all of them, resign) i can see them hitting the 10 year anniversary easily. red velvet are outdoing themselves with this comeback with physicals and digitals will most likely follow suit. mamamoo are also doing well and i don't have to mention blackpink.
for boygroups, bts, seventeen and nct show no signs of decline whatsoever.
i feel like 2nd gen groups were not as successful past their 5 year mark. of course, some (like shinee) are still extremely relevant, but most of them were not able to outdo their successes in years 2-5 later in their career.