I have to agree with OP, taxes should be based on weight. If you EV causes 10x the wear that a ICE car then you pay 10x the taxes. If the goal is fossil fuel usage, we cannot ignore the fact that pouring tar and repairing roads is not horrible as well.

If the goal is to encourage usage, then just subsidize it, but eventually it all comes down to wear and taxes, you cannot ignore a car that weights 10x as much as a normal car.

There are ways to make the road stronger if the government really cares about such things. But they don't it ends up being yearly cost = total upfront cost / average life span which in there mind is cheaper than a bigger upfront cost that lasts longer.