Is there some legendary USELESS and dumb car in Usa?
Ford Pinto is famously bad. Has a lot to do with it being unsafe (was known to burst into flames during collision), but it always tops the "worst car" lists. That would be fun to have, especially if they could program it to explode on impact.
I'm definitely with @grubdumpling on this one, I think the new trucks are right on, fun to use, and balanced. I believe I understand @justinlynch3 point on the default trucks if you use some of the better Russian trucks on the AW maps, so no disrespect, I do see how that would make it far too easy.
I'll add that I've been playing MR for about a year I think (on Xbox), and only since AW did I begin to pick up on the intended use of each vehicle type. Seeing how the skidder is meant to pull logs out of the swamp and bring them closer to the road, where you can then load them on a semi really changed how I play. I used to try to do everything with one or two trucks only, which also gave me the mindset that "many of the trucks are useless"... or more that only one or two are necessary to each map.
So AW has actually pushed me to play with more of a Hardcore play style in terms of Scavenging and using the Kiosks, and I find the game more challenging and rewarding this way. Each truck becomes more specialized and valuable in it's own way. Again, not trying to contradict the OP, just adding my experience with AW in case it helps anybody find more enjoyment in the game.
"Sandbox" refers to a world where you're free to interact with the game world on your own terms, and not obligated to take on any of the objectives. The world has it's own set of physics and other rules which still apply, but you can experiment and play within those parameters to your heart's content.
For example, you can spend hours experimenting with combinations of vehicles and trailers. I've seen videos where people load the car onto a small truck, then put the small truck onto a larger truck, and so on... just to see how many vehicles they can stack and daisy-chain together, all just for the fun of it. You'll never run out of time, the game will never force you to go deliver logs.
Hope that makes sense. Cheats or extras is a separate concept that, to my knowledge, don't exist in this game.