The fact that you can clear a tier on content after months of approaching it casually definitely does make it midcore.
Unreal and extreme are on the lower end of midcore, maybe the top end of casual. You can go in blind and clear in a couple of lockouts (or a couple of pulls in the case of Byakko). If you're unsure as to whether unreal and extreme are midcore, the problem here is your definition of midcore.
"Drop-in" content is casual content, not midcore content. Midcore requires some, but not a lot of, commitment. Midcore content is content that you can chip away at without having to spend much time optimising. Unreal, extreme and savage are midcore content.