Breaking the mold - as in doing something different from the expected and pushing boundaries. Fitting the mold - doing as expected, doing what others have done before.
Groups who attained success breaking the mold:
BTS - social media + "love yourself" concept for young people
()I-DLE - self-composing + "ethnic hip" concepts
Mamamoo - music/talent over visuals
(Original) EXO - dual-language concept
f(x) - Amber
Groups who attained success fitting the mold:
Twice
Black Pink
SNSD
etc