O'Rourke probably couldn't ride the anti-Trump vote to a win against Cornyn

Spot on.
I had early hopes for O'Rourke as the centrist candidate between Biden and Bernie. It didn't pan out as he was never able to capitalize on his earlier success in Texas. He has since taken all sorts of radical positions in an effort to catch the eyes of progressives, none of which would be popular if he ran against Cornyn.
Good coffee, good weed, and time on my hands...