Isn't it pretty unlikely that this debris, flying against the exhaust, can reach the engines with significant energy?
But looking at that pad and the damage to it- without deluge dampening, I bet the RC spalling might have been a bigger issue than just ground blowback.
Put a blowtorch to some concrete a and watch how quickly trapped moisture starts causing miniature explosions and flying shrapnel.
But that's just my first uninformed impression.
There is a reason that NASA dumps a few million liters of water under their rockets.
https://www.youtube.com/watch?v=jM61ZkUoO4U
> About 2 secs after starting engines, martyte covering concrete below shattered, sending blades of hardened rock into engine bay. One rock blade severed avionics cable, causing bad shutdown of Raptor.
https://twitter.com/LabPadre/status/1649062784167030785
is real, I guess not. What used to be in that crater couldn't just move sideways, it had to go up to get out of the hole. Engine exhaust hit the center of the crater, dislodged rocks, pushed them away radially and up the sides of the hole.
Four of the six engines later seen to have gone dark were in the outer ring. Coincidence?
The bells are cooled by pumping super cold fuel over them, a rock hitting those thin lines of fuel could rupture a line, or divert on causing a failure in the bell which eventually (seconds) ends in an engine rich fuel mixture.