Sure, I wouldn't expect fuel tax to cover everything. Local roads are quite useful to people who do not drive at all, and major roads and interstates are disproportionately worn by commercial vehicles that also benefit many people who do not drive private vehicles.
Indeed. After all, roads predate the car by thousands of years. But still, often roads are overbuilt and their potential capacity is never close to being reached. The bog standard suburban design we see in america for example is generally severely overbuilt. Plenty of arterials nowhere close to being used to their theoretical throughput limits. If your experience of suburbia is mostly american centric, if you look at say english suburbia where major roads only offer a single lane per direction you'd wonder how society there functions at all. But it does, because those single lane per direction have enough capacity to serve a generally denser version of suburbia than what we might see on the fringes of Dallas, where giant empty roads such as this (1; note how there are barely any cars in frame) are found on standardized 1 mile square grids out of routine more than anything really. Compare with (2) which feels much more right sized for the road demand in this generally denser suburban area on smaller lots with attached housing.