You really nailed it with this part of the thought experiment. A good plumber charges $150/hr these days. And $1500/hour is a starting point for better attorneys in certain cities. For a successful entrepreneur, the sky's the limit on what an hour of your time is worth.
There's an inflection point for successful business owners and some high-end service providers (consultants, attorneys, medical, etc), and some high-end skilled labor, where the normal things we do growing up, like mowing your own lawn, changing your own oil, etc, actually start costing you money to do yourself. It's one thing if it's an identity or values thing about doing it yourself, and are willing to eat the cost in what your time is worth, but it's another thing entirely if it's in an area that you just don't want to put the amount of time into in order to do it competently. Like load development. Or building your own house. At some point, it's not just an expense to do it yourself, but straight-up financially stupid.
That inflection point is different for each person, based on what their hours are worth to them financially, and what the trade-offs are.