Except Rubio has horribly out of touch positions that the Democrats can mock like they did with Romney AND still attach him to Trump AND he also has a very sketchy history in Florida.
Rubio's "out of touch" positions break back down into the simple left vs right political argument that empowers the elections and this very forum, so, can't comment such a broad subject here.
His character can't be attached to Trump and I'd argue a majority of national voters couldn't connect Donald and Marco. His history in Florida is for him to defend, whether that's sketchy or not is debatable.
Republicans are the ones on the losing streak in Presidential elections here. You can't just explain away issues where he holds positions opposite of a majority of voters as "well, political arguments." There's nothing about him that wasn't successfully used to scold Mitt Romney into defeat.
Rubio's character is also absolutely rotten to the core. He has odd relationships in Florida to incredibly corrupt politicians, is completely bought and sold to the Florida for-profit education industry, is a generally lousy Senator of no accomplishment, and seems to have no real principles other than he wants to be President and will say whatever the donors want to make them happy. His campaign message is also bland, forgettable, and resonates with nobody under the age of 60. He looks good in pictures, so people think he must be a good guy, but Romney was photogenic as well.
The more people get to know Marco Rubio, the more they will not like what they find.