I think Lind's point that if progressives dig in and defend Obamacare both as super-awesome and liberal, that they're making a big mistake, is important. The flaws of Obamacare are basically conservative ones. It's too complicated and it's too stingy and (happy to be proven wrong) likely won't cut overall medical spending much.
The point isn't "wah wah wah why didn't Obama wave his magic wand and make Medicare for all happen." The point is that we should continue to explain that Medicare for all would be better, cheaper, and more popular. Savvy people will inform me that Medicare for all won't happen and Obamacare is that best that could have happened. Probably you're right, savvy people! Congratulations on being savvy! I'm not sure why that precludes informing people that a better policy exists, even if it won't happen. Even savvy people spend lots of time talking about things that are unlikely to happen.