My problem with this process is that it's a low-volume, just-in-time system where you have to order the part, do the repair and send back your old part in a limited timeframe otherwise you are overcharged, not to mention the final step of having Apple support pair the new part to your phone to disable the warnings.

It's unnecessarily annoying and admin-heavy. Compare that to just buying a handful of batteries and keeping them "just in case" so you can then do the repair in your own time as needed. I currently do that but have to use grey-market parts as Apple won't sell them to me without the aforementioned restrictions.