Hmm, let's compare being a twohander in crpg to other mods
-In crpg - a twohander can wear heavy armor from the first round. Also, cavalry cannot outreach them and archers are nerfed so hard that they are less of a problem in general. Also being able to have very good stats (PS, Ath, IF) and very good weapons (Greatswords, Mauls, Katana, Flamberge, Axes, Bar Mace, Cleaver, Bardiches) and very good armor (Anything, especially a loomed set) makes them a true force to be reckoned with. Also note that, armor weights are halved. One example is Mail Hauberk (10.3 weight in crpg, around 20 weight in Native).
-In Warband native - Seeing a twohander is not very common. Seeing a twohander without shield+onehand is much more uncommon. Due to the reason that even heavy armor doesn't protect much and is helluva expensive to get. Cav can outreach you, and archers are super strong. Lowest damage short bow is among the best bows due to excellent fire rate. Archers are also very good in melee, meaning even if you can reach them they fight as good as any other infantry. Lower armor ratio also means, a two hander should be very careful at melee as well. Not very effective spam, due to the low armor ratio in general.
-In Ogniem i Miaczem (also known as WFaS) - Swedish infantry and muscovite troops have good two handed weapons and shield is less of a requirement due to the superiority of firearms. Yet, two handeds are very slow (around 90- 80 speed rating) to be effective spam weapons.
-In Vikingr - Twohanded (also polearm) is not very common still. There are no heavy armor, but every piece of armor is actually very heavy in terms of weight (a tunic has around 20-30). So that you can not ninja. Which means that you can not dodge ranged and have to rely on your shield against ranged (mostly throwing). Still, berserker class has no access to shields which forces them to benefit from their teammates' shields. Similiar to WFaS, those heavy long axes are far from being good spam weapons.
-PWmod - Two hander is very similiar to native here, unlike the armor ratio. But since this mod is not all of fighting, we can skip this mod. Yet, again everyone is forced to carry a shield when going into battle no matter what; or they will just shoot you.
Well, you might say that nothing is perfect. I say yes! Perhaps the other mods are not very good examples of a true balance, and crpg is the one should be inspiring them. But, ugh NO!!! The truth is, I've seen that twohandeds/poles can be very effective if you know how to use them in those mods. Besides no one is crying if they fail as a twohander. It's just that they are not an hardcore infantry class and everyone knows it. All in all (except WFaS), they have to carry something that should protect them against ranged and has to play extremely good/careful to gain the upper hand in melee.
If playing as an archer, shielder is frustrating until level 24-25 and even then, something difficult to benefit greatly at level 30; the two hander should be something similiar.