I couldn't even get through this entire thread. I made it to page 8 before the ignorance is was much for me to handle. Even if the hardness of the wood varies slightly between playfields it doesn't matter. The ball is harder than the wood. Its gonna dent. The size and depth of the dimple is going to vary by the force of the strike that caused it. This is why hammers are made of harder steel than nails, and why you use carbide to cut hard metals and diamond to cut carbide.
People claim their games don't have dimples but either don't post pictures or post a picture from a beautiful angle that has no reflections to show the unevenness of the wood. Astounding. I have 12 games, from many different eras and makers, they all look wavey/dimpled under the right light and smooth under normal lighting. I noticed this and understood what was happening well before anyone was crying about "dimples".
Even if you could get a harder clear coat, the wood underneath is going to dent and the clear will bend with it, or its going to crack, simple as that.