It seems to me that registration should be the point where a vehicle owner has to pay for public road usage. Some vehicles that need gas/diesel aren't registered for public road usage (e.g. farm equipment), and some vehicles which don't need gas/diesel are registered for public road usage (e.g. EVs). Therefore gas taxes are misaligned, but registration is by definition aligned with public road usage.

The only thing you lose out on is the fuel economy heuristic that bigger/heavier vehicles cost more to fuel (there's some physics to back it up: heavier vehicles take more absolute energy to accelerate up to a given speed, and an ICE only converts energy one way -- potential to kinetic -- so it's all eventually lost to heat via the brakes), therefore they'll pay more in taxes. But adding any kind of electrification into the mix (BEV, PHEV, or mild HEV) invalidates the physics behind the heuristic (electric motors can recover kinetic energy), thus the gas tax is supremely irrelevant and we instead need a different mechanism for funding roadways.