Man, this hits home because stuck fasteners are basically life in a nutshell. Everything feels like it's fighting you until you figure out the one dumb trick it wanted all along. Half of getting anything done is just knowing which way the threads run before you start cranking. My go to is heat and a good soak in penetrating oil overnight, then a dead blow tap before I even touch the wrench. Patience beats force almost every time, and force is what rounds stuff off. Same thing with people honestly, push too hard and something strips.

Get a caliper tool and check both sides evenly, because rust builds up on the rear slides way worse than the front on these cars. Your uncle isnt totally wrong for the old days, but newer cars with rear disc and traction control eat back pads almost as fast as the front. Next time just pull both wheels and measure pad thickness with a cheap gauge before trusting anybody, even family.