Trump is clearly not a perfect candidate. He is also clearly not part of the establishment GOP. Which out weighs him not being perfect in my book.
Frankly, the label has to be earned by actions over time that comprise a history.
Since trump has never been elected to anything, we don't have a history so we go with past and current statements. We see that from that he has in the past approved of national medical care and other establishment supported policies like government powers used to force the sale of property to developers, Close relationships with liberal New York politicians and the added bonus of financial support for them and any number of issues of this kind, although he now claims different views on some of this he refuses to acknowledge he had changed his mind. So in my view it's all irrelevant and should discarded as electioneering.
Rubio has been revealed to be not so much establishment but a lying opportunist who puts on whatever uniform is required to get favorable attention. Nuff said.... Karsick, (Kasich) Is indeed a establishment RINO GOP'er who has, along with the rest of the RINO's, become a moderate and essentially a Classic liberal, politically speaking.
Cruz has a history so we go with his actions (votes, speeches, statements) over time and we find that the establishment fears him, disdains him and literally hates him. so how is it that he can be labeled...establishment?
Of the 4, there is but one Reagan Constitutional Conservative that practices what they preach and that is Ted Cruz.