That is very true. However you can take a decent 7 inch lathe and tune it up to where it will turn parts without a taper. You still want your hub to run true as it can to keep wobble and vibration to a minimum. The larger lathes have more options available for them in the form of attachments and tooling is more readily available at very cheap prices. Power cross feed on the big ones is very handy. If all you intend on doing is prop hubs any lathe will do but if you want to do more bigger is better for me. But that is a decision left to the individual. You would be surprised at what you will end up making with a machine because you have one.