I'm no expert, either, I just read about death grip in Savage Love, and it always made me cringe and wonder, how in the hell? Then I learned more and figured it must have something to do with the skin being able to glide back and forth.
**Conclusion: **Based on histological findings and correlates of sexual function, loss of the prepuce by circumcision would appear to have no adverse effect on sexual pleasure. Our evaluation supports overall findings from physiological measurements and survey data.
It's not a question of enjoyment, it's a question of sensitivity. Dutch females statistically have a less sensitive vagina because of all the biking(saddles), but that doesn't have to mean they rate sex worse.
From what I understand, the penis is supposed to have a mobile skin system, so it can glide up and down. The "death grip" is when guys get a tight grip and crank it up and down to get maximum stimulation. Circumcision can (often?) remove the entire mobile skin system, leaving the penis skin as tight as the skin on, say, your thumb.
Get a tight grip on that, and start cranking, and it's basically trying to rip your dick off.