I did a voice memo test between the two microphones. AirPods and iPhone 7 mic.
AirPods definitely sound clear but not as clear as the iPhone microphones. But I wouldn't blame it on bad microphones. I think apple has done something with the software in these (noise cancelling, air beaming, multiple microphone inputs) which as a side effect causes the slight loss of audio quality. That being said during initial use I haven't had siri been unable to understand me...yet.
I would even buy these without the microphone, they're pretty great.
Can you compare to regular Earpods mic?