Stipulated, but I am thinking of the bigger logistics picture:
1. All other vehicles and almost all generators now use diesel engines and JP-8 fuel.
2. We are currently supporting dozens of "mini fleets" of specialized vehicles, which entails huge logistics and maintainance bills. Why add to the puzzle with more mini fleets? (On a meta level we really need to get our s**t together with trucks, LAVs, AFV's etc. before even looking at the ultra light fleet)
3. While an ARGO isn't very fast, snowmobiles are not very amphibious. Throw in tracks fitted over the wheels for extreme conditions (deep sand, snow, swamps etc.) and with the ARGO you have one vehicle that can operate in virtually every sort of terrain we are likely to encounter. The only vehicle that comes even close is the BV-206 and various related vehicles (Viking and ST Kinetics Bronco), which are much larger and more complex.
If we are going to spend a boatload of money for improbable vehicles like a Toyota Prius on tracks, then we might as well design an ARGO like ATV which addresses your concerns; higher top speed, Diesel engine with preheater and why not make it an 8X8 to carry a section's worth of kit and ammunition or 2 stretcher patients.