Yeah, I agree that Infantry is missing a middle ground option for the most part. In Warband, when choosing a loadout I would pick some form of medium armor and good offensive weapons. What I notice of most classes in Skirmish is that one handed weapons with the exception of Vlandian swords and Battanian swords tend to be smaller and swing speeds are generally slower. Currently the only reason to take light infantry is to sacrifice armor for cheaper units so you can have more lives and move around faster. However, if you are burning through lives quicker you mix that supposed benefit by spending more time to travel into the fight between lives as well. Whereas with heavier and tankier infantry, which some factions don't even have, you can stay in the fight and survive longer to potentially turn things around. Given the way things play out, unless in very specific and situational circumstances there really is no reason to use light infantry in Skirmish.
While Heavy infantry is currently typically the best option for an infantry player to choose both because they are well armored and get decent weaponry, their movement speed is a serious problem in that they are simply out maneuvered by both Cav and Infantry for the most part. Throwing weapons help with that, but if you eventually nerf those and don't fix the other issues with infantry they will be functionally useless for anything other than being a tanky hp pool to sit on a flag. They can't chase units down, their combat effectiveness is rather poor as well.
Giving faction a medium between those two extremes would do wonders to improve infantry play. Having effective weapons and while not having very heavy armor, a decent amount to remain a brawler. Some factions could use an entire infantry makeover, Khuzait and Aserai especially. The other factions would just need minor tweaks to their overall structure. I think the easiest way to accomplish that would be to give perks to the 2-hander classes so you can either go full on light armored 2 hander maximized for offense, and with perks have so if the player so chooses they could be the medium armored infantry with a little lighter but still decent shields and 1 handed weapons to cover more of the middle ground.