In my experience, it is not that hard to get a stream of fresh playtesters. Maybe I'm just fortunate. I also don't think the playtester bias to be particularly

In my experience, it is not that hard to get a stream of fresh playtesters. Maybe I'm just fortunate. I also don't think the playtester bias to be particularly bad for this. You'll miss some stuff because your playtesters will usually be a lot better than average at reading rules. But nearly everyone stumbles in visible ways on rulebooks, and the fixes for an experienced playtester stumbling tend to be simplifications / clarifications that are even more useful to inexperienced players.