Well, there's a bit more to a learner-beater than high action as you have mentioned - so, it could be possible that the action alone was enough to provide additional exercise for the muscles, but bad necks, rough fret work, poor tone, boat-anchor weight and general unplayability I would say in my experience as a teacher is an impedance to progress. Students have actually said they would have given up a long time ago if they had to carry on playing the "examples" they were told to endure at school.
That said, there is no doubt that after playing my high action bass for a week teaching, my gig bass feels like it has guitar strings on in comparison. Both basses are decent tools though.