That's unfortunate you feel that way. I guess it would be less bulky if it didn't have all the side storage. I felt like the Grip I owned was tiny, and the lack of storage definitely helped make it that way. I've never seen a Spinal Tap, so I can't compare those. I'm a big guy as well (6'3" 220) and don't really feel like the Flak is that bulky.
Yet, I'm on the Team, so take my opinions for what they're worth. I wouldn't be a part of it if I didn't believe in the products though. I'd still purchase a Flak3 if I wasn't on the Team. I've owned a bunch of backpacks, the Flak3 is by far the best all around.