I'll say my piece and the usual suspects can tell you how I'm full of it and don't know what I'm talking about but here it is:
First of all
this is NOT a borescope
Secondly, even if you were to use a real borescope (which would cost on average around $3k without an articulating probe and at least $10k with one) by the time you can visibly see something wrong with your valve your compression reading is going to be ZERO.
Personally I own two "scopes" The first is a
ProVision PV 300 Fiberoptic Scope and the second is a
Dewalt DCT411S1 and they are great tools for getting a serial number off of a hard to see magneto dataplate or for looking under the floorboards or inside a wing. Both of them will easily fit through a spark plug hole and with the clip on mirror you can look at the valves.
But the bottom line is, you're not going to look in a cylinder that has perfectly good compression readings and go "WOW, look at the big chunk burned out of that exhaust valve!" It just plain ain't gonna happen.
In fact you may have a cylinder with absolutely dismal compression readings that can't be fixed by any of the usual methods and when you pull it and look down there with the noonday sun at your back it's very likely that your naked eye will fail you and you won't be able to spot a single, visible thing wrong with it.
There, I've said it and I'm not going to say anymore.