Just because it isn't useful to the user doesn't mean some dev hasn't spent the cycles doing it. I know I've personally had to write code that was an absolute waste, but some PM wanted and it was coded. Usually so it can be a bullet point in a demo that impresses low skilled PMs or sales drone, but techy user types just roll their eyes when it's pointed out to them.

I think a mic visualizer is very useful to the user. You can tell if you're quiet, clipping, or your mic straight up isn't working at all.

You've moved the goal posts. Nobody said an input levels indicator isn't useful. We're talking about this specific graphic not being a useful graphic for visualizing live data. You've wandered away from the pack here

This was true pre iOS 18. The bars respond to the music now (at least on iOS)!

Ah, look at that, so they do!