It is interesting how flest does not require a definite article to be superlative, it is like saying 'I have greenest house' which feels very odd.
It sounds like an advertisement for an auto dealership.
Would it be right to say "Vi har de fleste biler" ?
That sounds more correct to me.
What does that mean?
My friends and I have five cars, you and your friends only have three cars, and a third group has three cars as well. Someone asks who has the most cars? My friends and I would say "Vi har flest biler!" because we have the most cars.