This lengthy article linked below was written in May, 2013 and presumed accurate, describes the complex history and dynamics of the Millard family. It might be that WM wanted to give his son what he never had, a rewarding and satisfying career to carry on the family tradition in the aviation industry.
I agree, WM had to have become increasingly aware his expectations of DM were unrealistic considering other people noticed.
“In his role as a business development consultant to Millardair’s new Waterloo airport venture, Al Sharif was happy to have only limited contact with Dellen Millard, the boss’s son and the guy in charge of hangar construction. As far as Mr. Sharif and other executives at the company were concerned, Dellen and his red mohawk spelled trouble.
“I thought he was just a spoilt little brat who had his way all his life and didn’t appreciate what his father was doing for him,” said Mr. Sharif. “He was an impediment to the hangar operation” who didn’t meet his deadlines, almost never arrived at work before noon, and refused to clear his collection of cars, jeeps, hot rods, jet skis and personal airplanes from the business premises.....”
Tim Bosma murder suspect, Dellen Millard made surprising decision to dismantle family business