I've had Moderna and the flu, and they were about equally bad ("I can move, but only because I'll wet the bed otherwise, please God let me sleep so it stops feeling like my bones are dissolving") but Moderna lasted only a day whereas the flu lasted several. I think you'll struggle to argue convincingly that Moderna doesn't commonly have awful side effects :P

You also didn't pass the Moderna side-effects to anyone else, unlike with the flu.