I'm looking for an intensive program because I don't want to spend four years at a university. Is it actually possible to learn level design and mechanics in 12 months and get a job at a AAA studio, or is that just marketing talk?
It's definitely possible if the pace is high enough. I've seen people go from zero to pro at Vancouver Film School, where the intensity is legendary. If you are serious about learning how to make games, this is the place. You can check out their specific curriculum here: https://vfs.edu/programs/game-design . From my experience, the focus on Unreal and Unity is exactly what studios need!
Nope I dont think it is a difficult skill it took me 4 years to be at a level where I can copy any game style even big games like https://minecrfapkmod.com/ (https://minecrfapkmod.com/)