Spinal Tap: Are they really that clueless?

Okay, so I finally watched "This Is Spinal Tap" and I'm reeling! It's hilarious, obviously, but I'm also stuck on something. Are they really supposed to be that clueless? Like, the whole Stonehenge debacle... Derek Smalls getting stuck in that pod... It's comedy gold, but are we meant to believe that these guys actually believe their own hype to that degree? Because, performance-wise, the actors walk this amazing tightrope. Michael McKean, Christopher Guest, and Harry Shearer are phenomenal. They're so convincing as these washed-up rockers, but there's also this undercurrent of genuine talent. Like, they can actually play, which makes the whole thing even funnier. I mean, that "Stonehenge" song is legitimately catchy! So, is it that their musical talent is overshadowed by their sheer lack of self-awareness? I'm especially interested in how Rob Reiner played Marty DiBergi. He's so earnest as the documentarian, trying to capture their 'genius,' but you can see the cringe slowly building in him. It's subtle, but it's there. Did anyone else pick up on that? I'm wondering if Reiner's performance clues us into how much of their idiocy is exaggerated for the camera, and how much is just...them. Anyway, super curious what everyone else thinks! Was this purely a mockumentary about ridiculous rockstar egos, or is there something deeper going on with the performances and the characterizations? It's been bugging me all day!