Hail dented my car. Which coverage?
Comprehensive. It is not a collision and nobody is at fault, so comprehensive is what responds, subject to that deductible. If comprehensive was dropped on an older vehicle, there is nothing to claim against, which is why that decision matters here.
The car drives fine but they called it a total loss. How?
Because the decision is economic. Extensive hail damage on an older vehicle can cost more to repair than the car is worth, even though it runs perfectly. You can usually keep it, with the salvage value deducted and a branded title afterwards.
Why is the repair taking so long?
After a regional hailstorm every shop is booked and parts are short. That is when rental reimbursement earns its cost, because the wait is measured in weeks rather than days.