There is currently no other option for consistent success.
Almost all the successful soloists are from the big groups, with a few exceptions for those that are mostly actors or have a long list of OSTs (more professional vocalists than idols).
There are some that don't quite fit the pattern, but they generally only have 1-2 hits before falling off.
Somi at first seems to be an exception, because she started her solo career years after IOI disbanded (existing for 1 year), and only had her larger hits 5+ years after disbandment. She's an exception that proves the rule though, because she was tricky and leveraged not only IOI fans, but also Twice fans (through Sixteen), Blackpink fans (through Teddy/TBL), and other fan bases through her friendships (e.g. Aespa fans through Giselle). Her recent flop with Extra is due, in part, to her promo doing almost nothing to leverage big group fan bases for the first time.
I think you need to go back to Boa for a clear exception, but I could be missing others.
On topic post from Somi