I guess what I sense about Rubio is that he really isn't "known" for anything . . . other than Gang of Eight. If he had all these great positions, where was he on leadership? Why did it take a Trump to say "halt Muslim immigration?" Why didn't Rubio kill the Iran deal, or line up forces to do so?
Govtrack.com ranks him pretty highly in “leadership score” which is measured by how many other Senators co-sponsor his bills.
But you’re right I don’t recall him leading the charge on any conservative issues. That’s a great point you could make.