Indeed the left currently has nothing. I still maintain that AOC is their brightest star, and that is really saying something.
2028 Republican is either Vance or Rubio, both would destroy anything the Democrats currently offer up.
Vance's fate is fully tied to the success or failure of Trump 2.0. Looking at a worst-case scenario, I'd say that any replacement level Democrat defeats him in a political environment like 2008.
Vance stands for doubling down on MAGA ideology (whereas Trump himself is more pragmatic and malleable) while giving the movement a friendlier face.
Rubio is an empty suit who will get fired by Trump within the next 18 months.