Wanting a QR system for my saddlebag that didn't leave scaffolding on the bike and was easy to transfer between different ones without having to buy extra mounts, I spent ages faffing around with lengths of bent steel rod, bungee cords, zip ties and heaven knows what. It worked - I got round LEL with it - but was never quite satisfactory.
Then I bought a
Classic rack. Some find it rises too far behind the saddle, but I've never found it intrusive. AFAIAC, it just works, and if you're otherwise happy with a saddlebag, I'd recommend it.
Releasing it and lifting the bag off is practically instant (unclip strap; lift); putting the bag back is a little more hassle (support bike from rear; clip rack into saddle loops; clip and tighten securing strap) but still only a few seconds and far, far less than feeding leather straps through saddle loops and back into the back of the bag.