Good riddance. I understand the whole Mii thing got popular and Microsoft wanted to chase that wave. But, they were just such an obvious "me too" addition to the XBox 360 at the time and coincided with Microsoft changing out the functional XBox 360 main panel for the ad laden shit-fest that was the newer designs. But, maybe I'm just old and hate superfluous crap between me and playing my games.
If you want worse, 15 years later, look at meta's avatars. They outright won't let you initialize your quest headset without setting up a meta account and one of these monstrosities. I shudder every time I activate meta's VR UI by mistake and have to watch at the creepy bastard in the customisation mirror.
These avatar things completely miss the point of miis. You didn't care that your mii looks stupid, the minimalist style pretty much made it a requirement. Yet they were a lot less creepy than all those discount cartoon characters with expressionless faces.
Plus the amount of bullshit customization meant you could make almost anything you wanted. Poofesure on YouTube's main Mii is named Beef Boss and his face looks like a hamburger.
When the Check Mii Out channel was a thing, I remember spending hours there just looking at all the crazy characters people had made. Peter Griffin, Batman, I'm pretty sure I saw a Ninja Turtle at one point.
EVERYBODY had the burger mii back in the day. there was also a classic gray alien and a comical looking michael jackson that practically everyone with an internet connection had downloaded from the mii channel.