Wish we had those shops around here. We don’t even have Costco where I live, and Walmarts are close to half an hour away. I’m not in the sticks; we just don’t have those stores nearby. Mavis, Monro and Indy shops are many around here. Despite memories of having issues with them, I sometimes wish we still had Sears automotive. We also used to have a Montgomery Ward auto shop, if I’m not dreaming.The good thing on flat repair at Discount Tire or America’s Tire is they’ll do it for free including a new valve stem and balancing even if the tire wasn’t purchased from them. They’d fixed the flat many times on my stock tires. Some forum members here even claim DT/AT will do tire rotation on their stock tires for free although I’ve never tried that as I can do stock tire rotation by myself.
I’ve been a faithful DT customer since 1980’s, and I’ve been going through the pro-rated mileage warranty credit process with DT many times. Of course it depends on the rep like everything else, but most of time the DT rep would start to urge me to get a set of new tires when the tread depth is at 4/32”. This means I can get 20% credit back from my original tire purchase price towards the new tire purchase if the 50K-mile warranty tires have been used for 40K miles at the time. I didn’t have experience on the uneven tire wear situation like you described as I keep up checking the tire pressure and tire wear all the time. All I can say is those DT reps are very generous on tread depth and they l’ll tell you it’s time to get new tires when the tread depth is at 3/32” ~ 4/32” anywhere on the tire tread.
And their 30-day free tire replacement warranty is real. Once I wasn’t satisfied on a new set of Michelin tires installed on my 2000 BMW 528i as they’re too noisy on the highway, they replaced them with another set but the noise was still the same. They replaced them again the 3rd time with Michelin’s but different model. That made me became a life-time DT customer.