You rub something enough times, something will bound to come off. Water drip on stone and after many years will still cut through the rock. That is why some old birds told us never to wipe lens element. Leave it as it is unless it affects your output image.
Lenspen is actually carbon that absorbs oils and stains. The coating will be intact since its soft sponge at the lenspen tip. To really rub until the coating worn off due to abrasive loss it takes a long long time and probably worn off many lenspens' sponge first.