My friend in Japan is telling me right now how TWICE suits the J-idol culture so well because of
1)their family like atmosphere,
2)their very different personalities and characters,
3)how they are relatable (the fun and not too surgically and skillfully perfect image)
4), and their colorful concept that's not too sexy or cute.
Their much better dancing is a plus. Screaming and belting like some k group vocalists like to show off is not a thing in the J-industry and TWICE members can all hold a tune, but with their own flair, which Japan likes a lot.
It's impossible for JYP to mess this one up.