Really regret not doing that myself.
Just using some back of the envelope math from numbers I found. On the high end a plumbing company is valued at 5x EBITA. A very very good plumbing company has a 20% net profit margin (and no debt, no corporate taxes or anything so that net income and EBITA are essentially the same), and a good plumbing company makes $350k in revenue per truck.
So a $10 million plumbing company would need to have 30 trucks, all with high performing employees. They’d need to bring in $10 million in revenue at best in class profit margins.
That’s a huge operation. Very few plumbing businesses owners will ever get to that level. There are 3 times as many doctors in the US as there are business owners with business that do the kind of revenue in the above example. If you’re capable of running an operation like that you can probably succeed at plenty of other things.
That said, I agree with your overall assessment that $10 million single-owner plumbing businesses are rare, for the simple reason that $10 million single owner anything is rare. If it were not rare, by definition you'd have a lot more folks worth $10 million (and, in this case, a lot more people lining up to be plumbers), and then $10 million would probably not be worth very much.
The thing to keep in mind though is we’re talking small business, once you get to $10 million EBITA, you’re probably talking $50-$200 million in revenue and 200-500 employees. Thats firmly into mid sized business territory and I think revenue growth would be the or primary driver of the multiple.
From your source a 10x multiple would require very high revenue growth. That makes sense because you can get 10% average return with index funds, so you need to significantly beat that ROI.
Or work in start up, get acquired, and chill after ?
The path I outlined in my OP is a _very_ common path that people take in Australia and not at all unrealistic. The barrier to entry is drastically lower, and the access to funding/capital is far easier.