I also found this to be true when using AirPods. When my gen2 AirPods are used as both the speaker and mic, everybody sounds horrible. But when I use my standalone mic the speaker quality is great.

I suspect something to do with Bluetooth bandwidth.

Also AirPods speech to text on iOS is unusable. There is a fairly 1-2 second delay before it actually starts recording what you said. But if you use the built in mic on the iPhone it’s just fine