So then you have another 20 minutes to diagnose. If you can repair 50% of boards that make it far enough that you need to dissassemble for diagnosis and then you take an additional 30 minutes to do the repair with 50% success rate, you're spending 3.6 hours per repair, which is perfectly fine if you're charging 300$. These are pessimistic assumptions too - you often don't need to dissassemble the board to diagnose it, the person disassembling the board doesn't need to be paid as much as the person doing the repair, and you'll probably have a better than 50% repair success rate.

Try linking to a video that doesn't fast forward the boring bits before doubling down on that 13 minute claim.