A 617 motor can be tuned for sure. More fuel, more air, more power, more heat, shorter engine life, that's how it goes. Not saying it is wrong, but if you want more power using more fuel, then why is it better than a gasser. The diesel by virtue of it's flat torque curve is much harder on transmissions, transfer cases, and driveline components compared to the sine wave power output of a gasoline motor. Not only do high output diesel motors have a shorter engine life, they compromise the reliabilty aspect that is inherent to the ignition free diesel engine design.
I melted a piston on a turboed 617 motor. The 617 engines lack the piston oil cooling ofthe 617a motors it's true, but it begs the question of why the Mercedes design team put a 617 motor in a heavy SUV when the 617a motor had been proven in the sedan models already. The answer boils down to reliability. Read Gary Stroh's book on his trip through Latin America in his naturally aspirated 300GD. Slow as hell, in low range over the high passes in Chile and Peru, but reliable as hell too. You hear people talk about the 300GD as the holy grail of Gwagens and as soon as they buy one, the shock of the first highway grade make them start talking about engine conversions.
I pulled big stumps with my 300GD on low range using both lockers, now I do the same with a G500 +/- the lockers. Both are great work trucks, the G500 is just not generally regarded as such because of it's luxury appointments and high price tag. IMHO, it is much easier to create a utilitarian high performance vehicle out of a G500 than a high performance utilitarian vehicle out of a 300GD, although both are possible.