? I think you're talking about JYPE where the whole 'Suzy bigger than Miss A' affair has traumatised JYP and his people so much that they decided to never ever let the idol get bigger than the group again.
As for SM, I don't see it: Yoona was bigger than the group when she had tv show super hit and started to be IT girl, and so far SM always seems to be pushing the most popular member at a time to get even bigger, providing more opportunities, gigs, CFs etc.
Which makes sense, if it helps a member, then it helps the group too - unless it grows into a Suzy vs Miss A situation, but that won't happen every time.
oh that applied to jyp obv, but they are not even trying to debut solos (yeji being the last one in years)
sm does but thats all, that as far as one can get and the debuts are always when the member loses steam and hype