Republicans WILL be the third party before too long, especially if they nominate Yeb.
Having so many conservative or pseudoconservative candidates in the GOP primary seems to be part of the RNC plan to coronate Jeb. Think about it: there are some liberal Republicans running who may take some votes from Jeb (Christie, Pataki, Graham), but their number and poll numbers pale in comparison to the split among conservatives and pseudoconservatives (Cruz, Walker, Paul, Perry, Jindal, Santorum, Huckabee). Rubio probably takes votes from both sides: some establishment Republicans, as well as some Tea Party types who aren't wise to him.
If there were a single conservative candidate as a Jeb alternative, he would win the primaries easily, but splitting it among a dozen candidates practically guarantees that we'll be stuck with him.