Not necessarily, it can mean disabling aircon, driving the lower speed limit, taking a flatter route, etc

It’s not always about quality or performance, you want cars to be comfortable too, which is why you have to make tradeoffs. One thing hypermilers sometimes do is taping the seams on the hood, door, etc to improve aerodynamics. You could make a car from factory without seams in the body, but you won’t sell very many unless you can convince people to crawl in through a window.

Other things may be prohibitively expensive, or not durable, so you make tradeoffs. As efficient as possible while staying within the chosen price class and providing a certain standard of comfort.

There’s a few diesel cars that can reach that distance on one tank (though it requires hypermiling)

I agree it’s safer to let them pass, but a medical (or personal) emergency does not give you the right to endanger other people on the road by driving fast and/or recklessly. That’s why they paint priority vehicles in bright colours and put flashing lights on them - to make it safer for everyone.

If you have a medical emergency, you call an ambulance. Yes, they will have to drive to you first, but care starts when they arrive. If the emergency isn’t big enough to get an ambulance, there’s no reason to drive fast either.