When you say commentators do you mean people mainly for the purpose of the stream or the players?
The way I see it is that when you have commentators their purpose is to help explain and point out exactly what is going on in the match and to therefore demonstrate to any layman viewer the "hype" behind the match and this kind of commentary is all well and fine, however
For the purpose of critique the commentators would have to shift and not only explain what and why they are doing what they are doing. But even in some instances what they should be doing. These too things are very similar and I know the overlap is great but I think it prudent to make such a thing abundantly clear first.
Edit : This would also mean it might be nice to grab a couple of gods around here to help on a specific night for specific players or practice on a specific match-up. (I believe Rsquared-sama would have no problems helping out a few labrys or red axing a couple of us as "MU Practice")