I do not believe the dimpling is due to the wood. I am a woodworker and have a number of hardwoods on hand, including, walnut, sapele, white ash (which baseball bats are made of), white (quarter sawn) and red oak and cherry. This is hardly scientific, but I dropped a pinball on all of the unfinished species multiple times from a couple of inches in the air and they all dimpled, including sapele, which is the hardest of the bunch. They didn’t dimple in the same way, but they all showed noticeable damage.
I dropped the ball on unfinished wood, but I also tested on a few finishes I use, including Behlen’s rock hard table top varnish, minwax polyurethane, hood finishing water-based poly and water-based lacquer. The varnish did not hold up as well with much deeper divots. I would expect this as varnish is not as hard. Both the water-based and minwax poly held up better with shallower divots. The water-based lacquer seemed to hold up the best, but there too I could see the impact from the ball.
The conclusion leads me to believe that it is not necessarily the wood causing the issue, but may be more related to the type of finish being used. Nevertheless, across the finishes, you still see damage.
I am thinking that the faster a game plays and thus the harder the ball contacts the playfield and the more airballs you get, the more you may see damage. I don’t recall many bw games having many persistent airball issues (I may be wrong) and they are not as fast as today’s games. My tspp, which I’ve owned since 2003, shows very little dimpling, it has no airball issues and isn’t nearly as fast as GB, Met or ACDC. My RS and wh20 also show almost nothing. I don’t buy the argument that dimples even out over time, no way that’s true.
Only the manufacturers know how their processes have changed and none will share it so we are left in the dark.