All valid points in my opinion. And you do tend to find older equipment used for the heavy stuff (Duffy is a great example, their biggest truck is 52 years old). I'm not trying to knock on Mack, but, I am saying that you could have gotten a truck from Peterbilt spec'd for the job. Granted, like you said, it would have an enormous price-tag, but, as you said, as well, any new Mack, Kenworth, Western Star, really any manufacturer, would have you over a barrel on price for something capable of handling the job (I believe that this is a large part of why the heavy hauler's run older equipment for the big stuff, it's simply cheaper).
I agree, as well, that a lot of people forget that a truck doing heavy haul doesn't have to be a hot rod truck. In fact, the law doesn't allow it, here at least, I beleive it's around 140,000lbs. gross or so you cannot have your truck doing more than 55mph, period. Driver's seem to get big heads about a lot of stuff, and most highway trucks will even handle grossing 130,000lbs. (granted they'll shake a bit taking off if it's a single frame, but, they ultimately will not tear themselves apart). What a heavy hauler should be, however, depends on what you call heavy haul. Is it 90k+? 100k+? 200k+? It really depends on where you draw the line. Personally, 100,000lb. gross is my line for heavy haul, and plenty of trucks will be capable of this, so, for those, 46k rears with a pusher axle is plenty fine enough. It also largely depends on the driver, as well. The biggest truck at Hi-Plains is the black and yellow 379. 20k Front, 20k. pusher, a 50k. rears (18 and a 625 Cat), which, doesn't quite meat all of your specs for heavy haul, but, he's grossed over 350,000lbs. with it (with the 10-wide he weighs somewhere in the range of 85,000lbs. empty). A lot of heavy haul is about the driver not the truck, just look at the guys who grossed 150,000lbs. coming up the Rockies in the '40s with 140hp. engines. Gearing, in heavy haul, is quite simply, the most important thing in my opinion. If you have enough gears and enough reduction you can move just about anything (look at the Space Needle: ONE horsepower engine, but, geared so incredibly low that it manages to move the entire top section).
This video shows how under-thought this job actually was, as I can guarantee you, if you had a similar truck to the one hauling right here had been pushing or had been pulling with the Peterbilt, it likely wouldn't have happened. You could move a 400,000lb. load with a bunch of dinky city-hauler's if you had enough of them strapped together because you're reducing the work each drive-line ultimately has to do (although, the more trucks you have to utilize ironically, you are decreasing the amount of work the trucks don't have to do because you're adding weight, kind-of an asimptotal sort of thing).
This is simply my opinion, and I will readily admit to not being an experienced heavy hauler, it simply deals with what I think from what I've seen and experienced thus far.