The party of Big Business, led by a putative Billionaire from New York aren't the Establishment?
Weird!
The Republicans have never been the Party of Big Business. The idea they were has always been propaganda thrown at them by the media and democrats, but if you actually go look and study the policies and effects of governmental policies on business you will quickly understand that the Democrats have long, LONG been the party of Big Business and the labeling of Republicans as them was just another form of them projecting.
To explain more fully: the main area people point to as why Republicans are for "big business" as Republican positions for lower taxes and lowering regulations, which are seen as them being "for big business" and again "little people." However, when you actually look at governmental regulation and taxation, there's actually a massive gap in which businesses are most impacted by those regulations and taxes.
Yes, big businesses end up paying less taxes and less regulations; however, the reduced governmental red tape actually allows small and medium businesses to more easily grow and end up COMPETING with big businesses. Conversely, when you introduce higher taxes and increased red tape, those small and medium companies often cannot afford to comply with them, leading to them going out of business and their assets sold off to companies that CAN absorb those costs, AKA, the big businesses. This actually creates incentives for big businesses to encourage a more strict regulatory regime and higher taxes up to a point (which, if you pay attention to DC, you'll note Big Businesses often do push for greater regulations and have considerable say in how regulations are written... while medium and small businesses do not... and thus regulations are written in such ways to favor those big businesses at the expense of their smaller competition).
No, if you look at Republican economic policy going back to their foundation in the 1850s, there is a consistent throughline: economic policies that favor the middle class. Sometimes this means trust busting, as Republicans have often done, sometimes this means deregulation, as is much the case now, but Republicans consistently have favored political policies that favor small and medium businesses and the middle class, while opposing policies that tend to favor big business and the monetary elites, since the elites prefer to have Big Business and Big Government working together to ensure their wealth and success, at the expense of everyone else.
