Graveyard cars is definitely NOT a top end body shop. They use as much mud as anyone, at least based on the little I’ve seen. I’m not saying they do bad work but there’s nothing special about their body and paint work, their reputation is the whole accuracy thing.
You can absolutely get cars completely straight with metal work alone. But the folks that can do that are hard to come by and the time it takes is not something that’s cost effective for almost every shop out there.
This is really unlikely. A guide coat is thin, you’re not going to make up the difference in a wavy panel with a guide coat. It will show you what’s there, but if it’s that easy to see the panel is wavy it won’t fix it.
And you can’t just block a car and fix stuff typically unless there’s just a huge amount of filler on it that’s “extra”. Even if they did it wrong but sanded til they hit metal you’d have to apply more filler to sort it out, just blocking it can’t fix it if the high spots are metal.