I find scanning QR codes at the POS hugely inconvenient compared to paying with my watch. The discount has to be substantial for me to ever scan them.

Retailer apps are often surprisingly (expectably?) bad at dealing with spotty/no connectivity, and even if they aren't, getting my phone out of my pocket, unlocking it, opening the right app, getting to the right screen in it (oh, did it just log me out?) etc. takes about 10x as long as arming my smartwatch in a convenient moment and tapping it once the terminal asks for it. It doesn't even require a free hand, since the range of mine is much better than that of passive contactless cards.

I like linking to the Amazon account because apart from the discounts (which are nice), it puts the receipt in my Amazon orders list. Yes, at Gus's there's no such linking feature or discount and I just tap my watch after selecting the appropriate card.

Amazon's app is just like what you describe. It is extraordinarily slow and needs a high-speed data network.