LownSlow,
It's how the aircraft has been since the early forties. 3500 hours later (of which 600 by me) no problems; at least none that are apparent. It's a bog-standard A-65. No major cylinder bore issues during last major. If your Cub was a J3, chances are it also had no filter when manufactured.
As I stated, there is no Arizona dust around where I fly, and I won't let you inject even controlled quantities of it near me!
Mind you, I do not do high static run-ups when operating from the beach, I always get the aircraft moving somewhat to avoid sand ingestion.
Loose grass just gets sucked in to the bores and gets burnt.
I agree with you on the thottle opening technique, my early hours saw a few sweated brows (cure: close throttle before prop stops, open again slowly).