I'm no transportation expert but.....
1) It's about 4.5 hours from LA to Vegas not six.
2) If you think about it from door to door it's probably a lot faster by car.
3) The more people in the car the cheaper it is per person.
4) While in Vegas you have your car for whatever. No car rental, taxis, etc.
I'm pretty skeptical but I've been wrong about a lot of things.