I have not played WC2, but its easy to see why humans don't use guns in WC3.
The dwarves already do. What would be the point in having two units doing the same thing? And the footman are hardly a waste of anything. They are durable and nearly immune to ranged weapons, and protect their ranged units better than any other unit. A wall of shields is almost unpenetrable, while you have dwarven guns tearing down opposing units on the other side and knights tear through the enemy like they're nothing.
Back in WC3, dwarven and gnomish technology wasn't widespread to the entire Alliance. Humans were still men in armor with swords sometimes riding horses, and dwarves brought their superior technology to the battlefield. Today, you see human footmen using every kind of weapons, including guns. They don't operate siege weapons, because they have been built for dwarf pilots. But even with that, you still see dwarven and gnomish technology being used more and more in the war, giving themselves a technological the Horde cannot match.
Like where in games does it shows that? And A gun special Gatling guns that they have WOULD be better then any infanty seeing as how they can tear down anything. If the Alliance are really that weak when it comes to melee then they should switch to a range offense like how we did in the real world. When you cannot train a warrior up anymore use guns to even up the odds. That way you dont need train a soldier how to fight just how to hold a gun, line up and fire away in rows after rows.
Using the hunter type of musket they should be able to reload quite a few time and fire volley after volley into the oncoming horde. The fact that they are using swords still is weird IF they are as technologically advance as you say.
I dont think there is one and I think the whole Horde fight better and Alliance have better tech is bull crap. They bought fight just as well and horde tech is actually a match for goblin tech. Sure it is dangerous but it is cheap and easy and can be mass produce, where as Alliance tech make sure their tech is more sturdy and reliable but are fewer in numbers.
Real life armies didn,t stop using melee weapons the second guns were invented. Even now, soldiers still have combat knives in case of melee combat, because there comes a point where your gun is not useful enough. Something you have to understand is that war isn't a matter of pointing and shooting. The most important part is discipline. When Orcs are charging down your line in a blood rage, it doesn't matter how many guns you have on your side. If one soldier loses its cool and runs away, the entire line crumbles and breaks. A line of footmen will do WONDERS to make the line of ranged fighters keep their formations and fire away. And those ranged fighters STILL need training, because otherwise, you're just picking up people and telling them to point, shoot and kill.
Do you remember how armies fought wars during, say, the civil war? They walked up to each other, while cannon fire rained around them, until they were in range, THEN fired. Guerrila fighting and taking cover wasn't part of the tactics like it is today. Horse riders could flank a marching army, charge them with swords, and be relatively unscathed by gunfire because those guns do little to stop a frenzied animal in full charge.
Now add healers and magic, and the guys who are charging are suddenly a LOT less vulnerable to gunfire.