I have to admit that diagonal wear like that is new to me, I haven't seen that one. But, I wonder, too, if maybe it's an indication of a worn shock? Sort of like how old tires used to "cup" around the edges with blown shocks. Maybe it's something to do with that?

Or could be a combination of things.

My experience comes mostly from performance tires in a performance environment. Things happen a little differently on an aggressively driven car that's wearing through a set of tires every 10-15k miles than they do on a "normally" driven car with 40k mile tires.

That RR tire looks okay to me. Maybe slightly under-inflated to cause the edges to wear more than the middle, but pretty evenly worn. I'm gonna bet they got their money's worth out of that tire.