Mmmmm...I'm not so sure about that. Both Cruz and Rubio have the same problem - they are both guys that have only ever wanted to be politicians their entire adult lives. They are both career politicians - albiet with much shorter careers than either Democrat. Cruz vs Sanders would be a toss-up but I don't see either getting the nomination. Rubio vs Sanders tilts Rubio's way, although the millenials might turn out for Bernie in unprecendented numbers. A Rubio vs Clinton would be "young inexperienced career politician with no track record vs old, experienced politicians with a long track record". I'm not sure that's a slam-dunk for the GOP. Neither of them is particularly likeable outside Team Party circles so the "likeability" gap will only be real for the partisans that aren't in play anyway. No play there.
Republicans will vote for whoever the GOP nominee is. Democrats will vote for whoever the Democrat nominee is. The election will be decided by the thinning group of independents and may well come down to turnout. THe Democrats have an advantage there in a presidential election year, especially with their leading cnadidates. Women will turn out for Hillary in unprecedented numbers and millenials will do the same for Bernie. In a year when the country kind of dislikes them all, that might be all it takes.