Right, we noticed similar findings. We do automatic punctuation now, and do diarization when there is more than one channel in the audio file. We're launching diarization on single channel audio with multiple speakers very soon. We're currently focused on improving some of our customization features, and then we plan to ship single channel diarization.

Thanks for sharing your results! We have more samples here if you want to do more comparisons: https://blog.assemblyai.com/2018/08/09/cutting-edge-phone-ca...