My method of making money is so radically different, I stopped trying to share or explain it.
I think your way has merit.
I think the important thing to understand is there is not "one way" to do anything.
We need to understand there is a cost per mile to operating a truck and trailer. We need to understand that cost varies based on age and type of operation. We also need to understand that the variable of a loan for this equipment creates an additional variable.
If you focus on cost per mile, it is important to maintain the miles needed in your calculations to make the math work.
If you focus on cost per day, make sure that the miles per day doesn't create a problem in the maintenance and fuel areas over time.
For me, I focus on 90k miles per year. It's something I can monitor as the year goes on, and a number that is easily adjustable. If rates are low, and it looks to be an extended low, I can up the miles. At the same time, I have to keep in mind the increased "per mile" costs that the operation takes on.
To totally remove the complication of things, for me, I fight for the best rates possible, as all should as far as I am concerned.
biggest mistake people who have no equipment payments make is not factoring in cost of the equipment. Your equipment may be payed off, but at some point you will have to replace it, or plan on greatly increased maintenance costs. When you are estimating your maintenance costs on old equipment, do your best to factor in odd repairs, and expensive repairs to the driveline, transmission, and gear boxes.
The one thing that often turns on owner operator back into a company driver is equipment that is paid for. That equipment breaks, costs are high, owner operator didn't plan for it, and either parks or sells the trucks and takes a company job.
Breakdowns should not be stressful. There should be funds set aside for this (not saving account). This fund should cover equipment repairs and salary during downtime. Salary should always cover you just as a paycheck would.