Oil refinery workers are generally college educated petrochemical engineers. Their "peers" in the corporate office often make much more than they do. I don't know of what refinery workers are "retiring early" but my grandfather's 30 year CITGO pin as well as cancer that runs through my family from proximity to those "low cost centers" leaves much to be desired of this rose tinted narrative you're describing.

An an engineer who worked in refineries in the US its pretty obvious to me that you haven't spent any time at all in a refinery or you'd know that the vast majority of people in a refinery are not engineers. They are pipe fitters, operators, electricians, welders, machinists, general laborers, managers, admin people, etc. Engineers are a small minority.

"Oil refinery workers are generally college educated petrochemical engineers. "

Alberta Oil workers are 1% 'petrochemical' Engineers. They are 'everything else'. Cooks, drivers, daycare workers, maintenance, carpenters, electricians, managers, team leads etc. etc. and earn about $120-200K, and while at the camp everything is provided for them in quantity (food is amazing if you like 'Denny's' kind of food).

I have read that most newly minted millionaires own their own construction/contractor business.

I can say, anecdotally, when I lived in Silicon Valley the blue-collar guy down the street had his own house painting business and did alright as near as I could tell. I know he got in a few hours of golf during most days.

Also on the golf course, realtors in the area.

This is the thesis of the Millionare Next Door and it probably still applies roughly adjusting for inflation, etc.

Another is if you take millionaire to mean “feel well off or rich” then being in a lower wealth industry will help that vs having everyone around you also be wealthy.

Many spend it all before they leave the job