One on one against Hillary even poor old Rubio does better than Trump. It is not going to be a cakewalk for him in the general.
You are basing this on a meaningless, hypothetical head to head poll on a contest that hasn’t even started. I don’t think any reputable pollster would assign any statistical significance to those polls. Reagan trailed Carter by ~30 points in March 1980. Was there any statistical significance to those polls? Should Reagan have dropped out in March because he was about to get landslided by Carter?