Go watch some rock crawling videos on YouTube. That's the kind of terrain legged vehicles are envisioned for. Making wheeled vehicles navigate that kind of terrain is non-trivial and requires lots of design compromises. There's a reason you see most people doing it in dedicated recreational vehicles.
>No better than a souped up ATV would
Big obstacles necessitate some combination of big tires (and all the big heavy parts to turn those without breaking) and massive amounts of suspension travel in order to maintain wheels on the ground (and therefore stability). A legged vehicle of the same weight would be able to carry much larger cargo or go over much rougher terrain because it would simply be able to step through each obstacle rather than roll over it.
>Probably worse, with harder maintenance and more breakdown potential.
Pin and bushings joints aren't exactly maintenance intensive and in "you should have replaced this last year" condition they tend to be more operable rotary power transmission systems. The problem is figuring out how to control the damn thing. Fairly recent advances in programming techniques (ML, basically) have resulted in new solutions for this problem which has resulted in renewed interest in legged systems.
>Doesn't matter, it's the concept itself which is nonsense.
There's a reason people keep trying to make legged designs viable. They're very attractive for navigating rough terrain because they offer the potential to do equivalent work with a smaller (and therefore cheaper and simpler to maintain) vehicle. It just turns out that every time someone has tried to build one the technology isn't quite there yet.