I admit I do think along the same lines as you on the point that it is fine having a high and low elo vs two mid elos, as long as the algorithm knows how to balance a high and low vs two mids, which I think it does from my experience. But I respect the thoughts to the contrary and essentially the developers with access to the entire database of games with all the stats such as game time will be the only ones who actually know.
However, I agree less with you and @twoofthegreggs also, that we can’t use extra information beyond simply only the TG rating to balance the teams. We neeeed them to balance team games better so that they are closer, and after factoring in the team game ratings they need to balance on the 1v1 elos. The end. So many times you’ll see the games landsliding because every person on one team has a higher 1v1 elo than the highest elo on the other team… I would go as far to say this happens more than half the time. And it is such a simple fix. We need these obvious trivial fixes.
And while I agree there are subtle differences between TG and 1v1, I find it very funny how you try to argue that this extra information carries no meaning because “1v1 skillset doesn’t translate to teamgames” 
Because they don’t know how to trade or teamwall or some logic like that.
Lets all pull together, there is a lot that can be done to improve the TG matchmaking issues… And opposing progress is a real shame