I'm going to partially disagree with you here.
I also mute the broadcast sometimes. Like you said, I'm watching. My ears don't need to tell me what my eyes are seeing. I'm not generally muting it because I don't like the play by play. It's usually because the color guy is annoying me or they are doing some other silly thing like Audra talking to a fan.
BUT
There are times I don't mute the broadcast. Like when Molitor is on. I could listen to him all day. I don't know what it is. When he's talking, I'm locked in and listening. Perkins gets closer to this than the other color guys, but still not on the Molitor level. The other side of the spectrum is Morneau. Awesome Twin. Great dude. But when he's talking it might as well be the Peanuts teacher talking. My brain completely tunes it out and it just become noise.
So, the fact that we are muting the broadcast, to me, doesn't say that we don't need broadcasters because I have eyes.... it means we need more consistently good broadcasters. And specifically here, I'm talking about the color analyst position. I think Provus does a perfectly good job as the PBP guy