I think that two things offset Underdog Armies quite easily, but both are in the hands of the host.
First is what does victory look like in the scenario? A few months ago I won with the Spanish against the French in the Peninsula. The French made a clumsy attack across some bridges, and the Spanish gave them what for, altho plenty of Spaniards decided discretion was the better part of valor along the way. I’ve had lots of success with so-called weak armies in all sorts of periods and I generally prefer them to the pressure of wielding the Imperial Guard effectively.
Second, Numbers. Closely related to the first, there are plenty of instances where the weak side could’ve come out on top except for poor leadership which the gamers can offset, and the proper use of numbers. I’ve won plenty of Flames of War games over the years with Italians, partially because people look down on them as an army and partially because hey, it is a POINTS system, and I will get more of my mediocre stuff while you have less elite stuff. That’s how the game design ball bounces.
So far, both sides have had solid performances, but I have not pushed the game design from FPW [which is pretty equal for wargaming] to Koniggratz and into Italy, but I expect Italy to play out quite well, really.
Finally, I think NT falls on his face somewhat with the scenario rules, which are too extreme. IMHO.