I agree that Rubio could win but only under a perfect set of circumstances. Anything can happen, but it looks like 2016 will look similar to 2015: job growth, but with lower gas prices on average. Assuming we have that type of status quo, Obama's poll numbers will continue to be 49-52% like they are now...I don't see how Hillary loses.
But if the economy starts to truly falter, a foreign policy disaster occurs, an actual Hillary scandal emerges, etc...sure, of course a decent republican can win. Rubio and Kasich are the decent republicans in the race - ie guys I can actually imagine becoming president.