aramis erak
Legend
Even with video; visual communication is reduced. My face isn't the most expressive... I do a lot with gesture, sign, and gaze. While ASL is possible over video, in my limited experience, it's like talking past a a mouthful of candy: Sure, you can communicate, but it's not natural in size, tone, nor expressiveness. (My brother-in-law is profoundly deaf, his wife totally deaf.) Even before I learned ASL, I used ASL-like signs often.I think one might be able to take advantage of a VTT to make processing math quicker, but I agree that (at least using voice, no cameras) actual play will be slower, because the communication channel/s won't have as much bandwidth as in person.
Also, there's the issue that a lot of subvocal audio is missed on VOIP.