Frankly speaking, most companies and groups most probably aim for mass appeal but I don't think it's essential for a group's success. It's especially not essential for fans unless they need validation for their music taste.
If a group has a certain music sound but fail to get mass appeal, I find it more respectable if they stick to that sound and harvest a niche for themselves that likes their unconventional sound than if they ditch their original sound and chase behind mass appeal and appeasing the public, even if they actually achieve it.
But I guess not all companies can afford being consistent and stubborn.
I just wish kpop fans would stop acting like mass appeal necessarily means better. There's no better or worse in this, a certain music style is not bad just because it's an acquired taste and has a niche following (sales) instead of mass appeal (streams)