I also pulled many Stronglight cranks off back in the day using the Park extractor, and never stripped one.

I didn't use the greatest of force trying to get a stubborn one off. I've seen guys break the handle off. If the crank seemed stuck on particularly well, I would leave the puller tightened in place and jump on the pedals with the crankarms horizontal, and after a few reversals of crank position and re-tightenings of the puller bolt, the crankarms came off with the Park puller.