The purpose of battle and siege is to win the round.. atleast for some..
The most interesting data would be distribution of classes on each side combined with result of round.
With a few thousand sample rounds I belive we could harvest some interesting results.
KD ratios are only indicative of usefullness.
Maybe not assign class to lowlevel chars (below lvl 25) just call them militia.
To assign classes , one should parse the logs, and count what kind of weapon each player used for kills.
If 25% of kills comes from crossbows and 75% comes from 1hand axe/1hand sword , then the player is labeled "1Hander with crossbow" and so on.. reverse 75% 25% "Crossbower with 1hand".
For most of the devs this kind of dataparsing should be 2nd nature.. im guessing.
I could take a shot at it if battlelogs were made available.
(Maybe clean out the chat, not everything said in rage needs to be carved in stone on the internet)