The more establishment candidates in the race the better. If it weren't for Christie, Kasich, Jeb, and Carly, Rubio rather than Cruz would probably be at #2. On the other hand, if Carson dropped out or his voters lost interest, I'm not sure where they would go. The more anti-establishment types may go for Trump, the more Evangelical for Cruz, while his PC establishment vote (probably about half of his support) would probably go to Rubio or Jeb.
In the early primaries it is important to keep the top positions (those who will receive a percentage of the delegates) in the hands of the non establishment. Yes it is important to keep as many of the establishment in to divide the vote so none of them reach that higher percentage