I've repaired/rebuilt all sorts of engines including everything from automotive, to industrial, to mowers to RC. Seeing deep scoring and metal transfer on the piston and cylinder wall is a very common sign of serious overheating. Dust ingestion could also cause some vertical scratching but I would expect it to be more uniformly distributed around the cylinder wall. If the engine ingested some sort of larger debris you would likely see some remnants of it and evidence on top of the piston.

Yes, there is some plating damaged on the outside of the liner around the exhaust port. Again, that is likely because that area got extremely hot.

This engine just appears to have been overheated for an extended period of time in my opinion.

Yes, there was a plating issue on certain OS cylinders but that was on specific models from what I understand and it was a while ago. OS makes an outstanding engine and the .46-AX is among their best. No engine, no matter how high quality, can withstand being repeatedly overheated for extended periods though.

It's just an example of learning the hard way. We've all done it in one form or another.