So how many times a day am I told that the Congressional Democrats can't be all left-wingers because a real left-winger can't win in vast swathes of the country and so we would be in the minority and then what?

The answer is, I hear it a lot! My argument is, being more left-wing would make the party more effective on a per-congressperson or -senator basis. The Republicans accomplished almost their entire agenda when they were in power, and even now, when they are in the minority, they can have a great deal of influence over legislation. This is because they are more ideologically uniform and extreme with a few exceptions. They are also more dedicated that the Democrats, which I think goes along with the uniformity and extremity. As a rule they don't need to compromise with each other. Therefore they are able to simply act, rather than begging dozens of collaborators in their own party not to shaft them.

Right now there are 255 Dems in the House. Would you  give up 35 of them to get 220 actual liberals and leftists? I would. 220 is still a majority, and with a majority of legitimate Democrats there would be nothing in the way of progressive legislation.

The Senate is more difficult because its rules are designed to keep democracy from working. But with 56 Dems in there now, I would trade the current situation for a Senate with 51 progressive Democrats.

Maybe you like different numbers, but my point is, there's more to it than the numbers. Once you have a majority, the value of adding to it starts to diminish, especially in the House. I understand the fifty state strategy and what it accomplished. But I don't think that we actually gain by adding a Republican to the Democratic majority. It makes it harder for the actual Democrats to solve problems, because there's always some fake there in their meetings screwing things up.