Fact: There is no head to head match ups until past Super Tuesday primaries are over. Especially not Trump versus Carson. Because Bush, Cruz, Rubio, Kasich & Walker have enough money to last through super Tuesday.
Which means Carson would have to win over all of the candidates, which is unlikely. So Carson comes out of Super Tuesday with no wins, but a collection of delegates because many primaries are not winner take all.
After that stage, many will drop out and also could Carson. If present trends continue, there will be 3 candidates fighting it out for the last half of primaries. Trump, Bush, Cruz -or- Trump, Bush & Kasich.
If Cruz remains, Bush wins.
If Kasich remains, Trump wins.
Your points are well taken. However, as of now, Carson is a tad bit ahead of Trump in IA. If he wins the first contest, he could build momentum and go into the Final Three.