I don't know if it depends on specific models because some people seems to be using Macbook Pros without headset and their voice is crystal clear while other seem to be talking from an old airplane microphone.

Anyway I guess it depends where the macbook is positionned. I am not using a macbook but my laptop is stashed away on a shelf[1] when plugged to my usb-c docking station using external screens so using the embedded mic would be a no starter anyway.

[1] it seems to be cooling and running quieter vertically when its bottom fans aren't obstructed.