So the zinc actually bonds to engine internals and creates a wearable liner?
Is this purely preventative? Would it ease the suffering of already worn parts?
Yes. Yes. And yes! The zinc both prevents wear in the beginning, and plates the wear marks over time, making an oil-holding surface that is very slippery, and can be downright hard to remove from the parts if built up thickly.
The AMSOIL-laced engines (AMSOIL has lots of zinc in many of their oils) I have seen (in the 750) have this buildup: the last one like this that I rebuilt had 62k miles on it, but the entire bottom end looked and measured brand-new, even the primary chain. It took a week of soaking in xylol to get the parts clean enough to be sure my measurements were true, and I have to say I am impressed! Even the clutch plates were only 20% worn at that mileage, and this engine was virgin when I got it. The engine is a K2.