So watching a Raden clip made me think about this again
You're thinking too much. It's inevitable that models will share similarities when everyone is drawing from the well of Japanese culture and history to inspire their designs and there are so many vtuber designs being released. There are only so many meaningfully different colours you can pick for hair and so many meaningfully different body shapes you can pick from. If there are similarities, that's just a product of the sheer numbers involved.
I was thinking more about the style of the art vs. the theme of the vtuber. For phase, the gapmoe of the character and the style of the art has had a positive influence for "pink rabbit" and "angry business suit fox". Lia changing the theme of her model vs. Lumi changing the style of her model is an ideal example of character vs. art. Some character art leans into tropes like Michi's big ass hat but others flip the script like Nasa having dragon hands. Unless the person is entertaining none of this matters but it's hard to know what people will become fans of.
Phase doesn't have to budget to blow on redesigns left and right like Cover with Irys - I still think her original model is outstanding - and others like Vesper/Magni/Nene/Flare etc. The Regloss model themes are pretty plain but the art style plays a big part in distinguishing them.
Ao - Manga character style
Kanade - Clean illustration
Ririka - Also crisp illustration
JFT - muted version of their art - see
Suntory Nomu
Hajime - Bright, somehow not oversaturated illustration
The makeup for JFT being obvious, the glow of Hajime and the mature eyes of Ao set these characters apart at first look. Kanade and Ririka are left to their personalities. These illustrators are all amazing but think about if Kanade and Ririka didn't look like characters from the same show...
The timing of this Phase generation seems really good though! Their character art make them seem like characters from the same show but that's OK as personality is key. I watch too many JP streamers and I am still really excited to see these new girls. Big wish - off collabs....
TL;DR Character design can synergize with or elevate a talent. The new gen might not get that boost as their character art has a similar "look and feel".