I don't say I am against this idea, because this would be wrong, but I am not for it either. I just think it won't be that interesting, and thus it's not worth the effort to be implemented.
I am a huge fanboy of teamplay and tactics, so this mode wouldn't be my cup of tea anyway. The problem I see with it is concerning the classes. In my eyes, everything except of 2 handers (inlcuding poleaxes) and 1hd + shield would not be that viable for this mode, simply because those two classes are the most viable ones.
All ranged classes would have the problem of limited ammo, but changing this would result in a huge amount of ranged spam, at least compared to the actual amount of ranged fighters. (Still it wouldn't be as many as on the other game types).
You already said that horses wouldn't be allowed, so you wouldn't have 1hd/2hd-cav, lancers, HAs, HXs and HTs any more. Pikes and hoplites wouldn't work at all, so they would disappear, too. Throwing would also have major problems, next to crossbows.
You would end up with mostly heavy infantry and a few archers.
The fights would consist either of picking your enemy and hoping you don't get backstabbed while fighting him or looking who's busy fighting and trying to stab him into the back, running away if he turns to you. Depends on what plan you are following.
It would basically be like a duel server, but more chaotic, and with less messing around and "experiments".
I don't think this gamemode would have many players, nor would they play it for a long time.
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