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In idol groups, you will typically divide the proposal of a group on a balance of "Cool, Sexy, Cute". And as far as vtubers go, that was the mentality inherited.
However, as time went on, I think it clearly shifted to the division of a group you'd see in anime, the "PrettyCure/Azumanga" division by age (Mature, Youthful, Childish) which is relative to role not actual age (in precure gens its typically a 12-16 age range, but in other anime it can be 14-22 for example)
This could explain why so many people have strange feelings towards Council as a group. It has a great balance of the former, but its one of the few holo gens that is very unbalanced in the age presentation aspect, with too much blending together at the middle and a notable lack of a more childish talent in body and soul.
I think its particularly striking since the meta vtuber balance is the opposite, a gen with 2 matures, 1 youthful and 2 childish.