Ugly GRX RD failure...

[Hank Scorpio]

Looking at picture 2 there are definitely scratches in the lower pivot of the body although none on the cage. Can't tell how it would get scratched so heavily in that one location from a fall and nowhere else. Maybe if it happened while it was on the big cog in the back that kept the cage off the ground?

[dddd]

Derailers get torqued rearward from spoke contact often enough, but another failure mode with a similar outcome is from the chain seemingly getting derailed off of the top pulley and jamming, then typically "lacerating" or "chain-sawing" the cage plate at that location to some visible degree as evidence.

In this latter scenario, it's not torque being applied to the derailer cage by the spokes that does the damage, but chain tension that pulls the derailer cage around with the rotating cassette (seemingly the cause here because the OP mentioned the rider not needing low gear when this occurred).

As for a too-tight chain, are there any derailers from the past 30 years which can't move fully out of the way of a full-tight chain[?] (not to say that a too-short chain won't cause damage to any number of other parts, including the frame, and which could perhaps damage the derailer itself as a consequence of other parts failing).