Again, for around a century, the fuel tax has been transparent. I don't see how a mileage tax which you have stated would have to reflect the size and weight, so would be different for differing vehicles is more transparent? Add to that it is not collect or billed in small amounts is preferable. Fuel tax where the tax is billed at purchase, (monthly for most electrical customers) handles that easily.
One thing that hasn't been said. Any change from a fuel based tax is going to require a change for EVERY vehicle. We will have ICE vehicles on the road for the foreseeable future. A mileage tax requires a tamper proof measure device, something most ICE vehicles have only recently had. My 1942 pays its fuel tax even without a working odometer.
A KWh tax would require no change for the majority of the vehicles in use today. As electrics gain market share they could be "brought into the fold" with a Kwh tax. So a Kwh tax would be easy to change too. The less the 2% of cars on the road today that are electric can be assessed a flat tax as they are now until retired or retro-fitted to supply the needed info to the power provider.
It is a proven system of collecting taxes, its weak point is the unwillingness to raise the tax to cover inflation and the dipping into the funds collected for other non road uses, something that any tax is subject too also.
The thinking that we must tear down the system and replace it, doesn't make sense if you are doing so for the stated reason of maintaining roads. I have not heard of any proposal that would not fall victim to the same "failure" that their proponents claim they are trying to remedy by abandoning the fuel tax.
A mileage tax alone isn't as fair as a fuel tax. It has to account for weight to do so is more complicated. Fuel, be it fossil or electric automatically charges larger and heavier vehicle more.
By moving tax collection to the power companies, you don't have every owner having to file a report and pay as a separate operation. Something the framers of the fuel tax reasoned when they collected the fuel tax at the point of retail sale. Far fewer actors to look after. Nothing is perfect, and their have been retail sellers prosecuted for not reporting and submitting the tax, but they were caught, something much easier to slip thought the cracks if it becomes each individual.