Assuming Elizabeth has a fairly low ceiling (NB this is my biggest assumption and one I am not sure of), the field is so divided that a unifier who stands out on the surface features (appearance, articulateness) and can bridge some of the policy gaps (e.g., "Medicare for All who want it") is in prime position to open up a lead and never look back. Buttigieg is the only one I can see pulling it off. Can you imagine anyone else pulling way ahead and never looking back?
I think Sanders and Warren both have a much higher ceiling than you think, and their (imo, wrongly) perceived electability issues is all that's holding more people back from their side. They can absolutely keep winning people over on policy and integrity, and they represent a version of the left that's either going to be the mainstream now or later. It could be similar to Trump in 2016, where despite the initial logic at the time, he actually spoke to the republican base better than Cruz/Jeb/Rubio/etc. As the electability issues go too, Sanders is pretty clearly only second to Biden right now in general election polling, so it'll be interesting to see how the media covers that if Biden starts averaging below first place.
We can agree to disagree on this. But I think it's naive to assume voters will flock to a currently second tier choice when Biden falls and others drop out, if there are already other frontrunners they can get behind who they can push ahead.