This is my first post here, so pardon me if I'm retreading old debates. I just have the vanilla game, but I absolutely love playing with the VEM, and the vanguard unit line is a big part of the reason why. That said, I think it can be improved.
First, I suggest you modify all the ranged units to have a range of 1, though with some improvements to their melee combat (defensive) ability. Though that might make archers seem more like regular warriors or spearmen, in practice it should mean that mobility becomes far more important. A player could build some archers as a defensive force, but they wouldn't be able to concentrate their fire on a single enemy from afar, they would instead have to move and flank the intruder. Likewise, an attacking spearman facing an archer on good ground wouldn't be certain of victory, they would need a flanking unit providing support or softening up the target for success. So limiting the range of the archers opens up an important role for a highly mobile light infantry unit (it also, coincidentally, makes cavalry and siege weapons more useful).
To keep things simple, I think we can then make the scout, and the vanguard/light infantry line that follows, all ranged infantry. Give the scout a weak ranged attack, and then allow them to upgrade into archers. Archers, with only a range of one, are no longer the foot artillery of the vanilla game, but true light infantry, good for defense, skirmishing, screening, and scouting. Different promotions could specialize a particular archer unit as a scout, skirmisher, or defender.
In battle, as it happened historically, archers would harass the main body of the enemy from the flank, or would be simply used as fodder (like helots or velites) to soften up the enemy before the line of spearmen or swordmen closed in. With the Recon 1 promotion mentioned above, they could also play a sort of defensive guerrilla role, harassing a column of enemy soldiers trying to make its way across difficult terrain. Cavalry would be particularly useful in screening infantry from such harassment.
The big change, though, would be with gunpowder. I would allow the new light infantry line to upgrade from archer to xbow to musketmen, with the musketmen changed into a ranged unit, with the same 1 tile range as the new archer and xbow. The musketmen would thus be very good for defense, but for offense you would either need to concentrate massive numbers of them, or use cavalry and cannon. Longswordmen, though, would still be the most powerful infantry attack unit, next to Pikemen. So for a while, armies will be mixed pike-and-shot.
Eventually, though, armies will become mostly musketmen, and defense will take the upper hand. It will be difficult to storm cities, at least not with lots of cannon. To take out the cannon, and to cut through the lines of musketmen, we'll need a faster, more aggressive cavalry unit - the Lancer. (Modern Cavalry becomes a more mobile sort of light infantry, with single-range attacks).
As the infantry progress, they're all basically acting as light infantry, but it might make a better game to split them back into melee/shock troops (grenadiers) and skirmishers. But I think we should keep the gunpowder infantry as single-range units. It would be more fun, I think, to let the vanguard/light infantry units to upgrade as cheap, irregular, militia-style units, and keep the regular infantry as heavy and expensive. As these units become more powerful, wars should evolve into fixed-fronts like in WWI, with lines of infantry struggling to break through. Massed artillery helps a little bit, but it's only with tanks and aircraft that the offensive regains the upper hand.
From there, the heavy infantry becomes mechanized, and the light infantry becomes special forces (both now as melee units, no range). The advantage of special forces, besides air mobility, is that they do better in woods and mountains, and away from roads. The proper role of the special forces then, is to guard the flanks of the main army, and to destroy strategic resources and artillery/anti-tank guns.
So, in sum, I guess it's not just about saving the vanguard line as it about replacing the vanguard line with a more fully realized archer/skirmisher line, and keeping that distinction alive through the gunpowder age. Thanks for reading all this mess.
