Creaming off a nice profit from our postage money is one thing, but couldn't they have found an easier way to do this ...

Yes, they could have found an easier way - seller fees for private sellers - just like it used to be in the olden days before eBay started to offer regular promos for 100% or 80% off fees, then wall-to-wall sell for free.

When I sold as a private seller, I paid FVF fees and optionally, I could pay for more images or gallery pop-ups.  I didn't have a problem with this, I understood that I would have to pay for access to eBay's footfall.  Nothing in this life is free.  

All eBay had to do was re-introduce FVF for private sellers - but they didn't.  They could have offered the option of simple delivery for those sellers that preferred buyer fees and no-hassle QR code labels - but they didn't.

IMO, a massive own goal for eBay.