EMs have extremely slow ball speeds and almost never have a ball hop off the playfield. Of course you'd expect them to have less dimpling.
William/Bally pins have noticeably slower ball speeds compared to modern STERNS and much less air balls resulting in less dimpling.
STERN gamed have faster ball speeds and as a result usually more air balls which will result in more dimpling.
I bet if you took a Williams playfield at the time of manufacture side by side with a good STERN playfield and repeatedly dropped pinballs from the same distance in various locations you'd get the same results.
Ball speeds are faster on modern pins, air balls are more prevalent, which all means more abuse on the playfield surface. Personally, I prefer faster pinball and can live with some dimpling.