Look, as mentioned elseware, you could write your doctoral dissertation on this subject.
Learning from the past, and preparing to fight the last war.
We frequently build the army to fight the last war, which never seems to work, but yet or magical future seeing crystal balls don't work either.
In the napolionics, long arms began to dislodge cavalry but even then you blast a formation of infantry with your artillary then let your cavalry at em. By the time of the civil war cavalry was really mounted infantry, and that was using old for the period longarms. Repeaters were present but ignored due to lack of very long range capability. Even Custer's men turned in their spencer repeaters for sharps carbines under the concept of open warfare in europe the 45-70 could be volley fired at a clump/column of enemies.
WWI comes along and teaches us that nope, infantry units taking long distance shots at eachother is a thing of the past, because lets say your 45-70 can volley-fire a mile, and his 7mm mauser can only volley fire 1/2 mile. You sit around volley firing your 45-70, he calls in artillery. OR, you get closer, say 300 yards, then his flatter flying cartridge has an advantage.
Of course, machine guns ruled the front, you hid in trenches to avoid them, and tanks were invented to counter them.
But really, it was biplanes guiding artillery that mashed stuff up.
Then came WWII. Better bombers and artillery meant trenches didnt' do a whole lot of good. But then we spend more time on fighterplanes to protect bombers, AA guns to repel them, artillery-counter-artillery meaning you fire a few rounds from your howizter and now the enemy knows where you are, so they shoot their howizter there, so you better move.
So we build this huge war machine that is 3 or 4 degrees away from the actual infantry. It doesn't matter what gun the infantry has when the bomber hits them. It doesn't matter what bombs the bomber drops if the enemy fighters intercept it, and if those intercepter fighters are junk compared to escort fighters etc etc.
So the USA builds it's modern army around air craft carriers, tomohawk cruise missles, M1A abrams tanks, Apache Helos, etc. Yea, when those beasts are in theatre, it matters not what guns your infantry has, or what guns your enemy has...as long as we fight under their umbrella.
However, the enemy will of course go to long lenghts to avoid this. Also politics gets involved and messes stuff up. Vietnam, check out the movie and book 'we were soldiers' Our artillery and planes kept many many enemy at bay, or else they attacked at night, or tried to rush to get in too close to use artillery.
The other tactic is to attack at two spots, make them send all the planes and tanks there, then go attack somewhere else now that it is free of them. This also happened a lot, when there were no planes available for fire missions, and artillery was tied up elseware. Part of this is politics, and the other part is politics too!
The first part is simple and clear politics, they don't want to send in more troops or more gear, even if it is present. (example, no tanks in somalia, it would send a bad message! also said no to a lot of tanks in Iraq cities right after the actual Iraqi army was beaten in gulf war 2)
In WWII, the german tiger tank was much much better than the sherman. One Tiger vs 2 shemans was a fair fight, maybe. Good thing we could build 3 shermans for every 1 tiger.
Yet nowadays we invent a bigger badder whatever, and where we used to have 12, we now just get 8 of the new one, because that is the 'same amount of force'. You do that enough, you got a handfull of super killing machines, but they can only be at one place at a time.
Back to the Somalia example. No tanks for political reasons. Okay, lets say they change their minds, which is better there? A single M1A abrams, or 12 sherman. A single abrams could take out all 12 sherman no problem, but a single abrams can only be at one spot at a time. If the Abrams is there, the enemy doesn't even bother, it just attacks where the Abrams ISN'T. But a Sherman vs a bunch of guys with AKs, recoilless rifles, RPKs?
When the enemy comes at you in waves of men like it did in somalia, during some parts of the vietnam and korean war once the units in question had limited support, you sure as hell want your 4 man fire team to be 2 assault rifles, 1 assault rifle+grenade launcher, and 1 SAW/light machinegun. (or more light machineguns) all using compatable ammo, and then more shots per pound of ammo was a great thing.
Now, in Iraq and Afghanistan, it has flipped the other way. There are no spots where we are short on air/artillery support (or so it seems to me) so the enemy cannot attack in waves because our heavy ordinance would rip em apart. Instead a handful of guys shoot at you from the extreme range of their weapons. In that case, having some longer range M-14 type guns would be great. So do you redefine the fireteam to eliminate the SAW as 1.) ammo compatability isn't an issue, reinforcements and air power will come before you run out, and 2.) probably no human wave attacks, and in it's place have a single long range weapon? That would probably work right now in Iraq and Stan pretty well.
But would it work well in the next conflict, against say North Korea, China, Iran, etc where again we might spread our handful of uber warmachines out too thin, and the enemy will attack with waves wherever our ubermachines AREN'T, and in that case you want the SAW back, more ammo per lb, and ammo cross compatability again.
As far as the enemy using assualt rifles. Hell, the enemy in somalia would probably have been better served with a PPSH-41 just as effectively (you know, soviet SMG, 71 round drum, 7.62x25) In Iraq now, you'd probably be better off firing your pot shots with an old mosin-nagant, it will go through more of the armor our troops wear, and it would outrange their 5.56 weaponry. Humm, maybe if you duct-taped a PPSh onto your Mosin....
