Well, large scale wars are on the way out...
What makes you say that? It's been more than a decade since the last one, but I would say it's only a matter of time until there's another war with a 1,000,000+ body count. Does the recent civil war in Syria that's lasted for about 5 years not count as a recent, large scale war? How many people need to die until it counts as a "large" war?
It's the same progression downwards which has been happening through the ages.
Massed infantry was ruined by the invention of automatic weapons. Now, with the invention of all manner of battlefield controls available to us, any infantry that are even known about can be easily cleared out.
Face it, one squad of SAS with full "missile artillery, attack helicopters, battleships, and unmanned aerial vehicles" support will wipe the floor with as large of a standing army as could be called in.
Infantry still have their place, but their place is to be the man with the laser light, marking targets for everyone else.
The only thing 'large force of regular infantry' is doing in Afghanistan is cop-work.
There are counters for all of those controls you mention. And infantry no longer march in closed formation, but nonetheless their numbers remain quite large. Automatic weapons are force multipliers, they are not direct substitutes for manpower. Battlefields are much, MUCH larger than they were in the past, so you still need all of those people to cover all that extra ground.
You could not be more wrong. It is impossible for...I don't even know the order of battle for the SAS, but let's just assume a squad is 12 guys. It is utterly impossible for 12 men, regardless of who they are, to win any kind of war no matter how many bombs and gunships they have behind them. You've been watching too many Hollywood movies.
You're not wrong, but the war in Afghanistan is not being waged against a conventional force, and as such should not be used as a yardstick to measure how every future conflict involving the US Army will turn out. There hasn't yet been a war where all the recent modern firepower of first world nations have faced off against one another, but men train for it every day, and when that day comes, there will be a great need for the scores of riflemen and their ability to be in a lot of places at once. I'm not saying that there is no place for special forces in war, but there is no such thing as an entire army composed of elite forces.