I'm not sure I understand what you're trying to say, but you have clearly made RJ's point. The limitation on this dive is the bottom gas not the deco time. As such RJ has used an extreme example to point out that at this depth the average diver can not safely generate enough deco obligation to justify the need for a second deco bottle.

I would hope technical divers would have better than average SAC rates.

Personally, RJ's example would be the limit of my 1/3 reserve (assuming 120s and a 30 cf of 80%).