I think spears should be balanced according to their historical effectiveness. The problem is, no one knows for sure how effective they were in history.

I'm not really interested in discussions about "balance" that pay no regard to history or plausiblity. Why play Medieval Total War at all, if you don't care for the realism - just find some arbitrary rock-paper-scissors game and have fun tweaking it to be perfectly mathematically "balanced". (I understand balance is important in MP, but there's another forum for that particular discussion.)

Personally, I think it is fine that a well armoured knight who has trained for combat all his life and has a big strong horse should be able to beat up vanilla militia spearmen. I've read an account of a handful (I think it was seven or so?) feudal knights defeating about 100 Welsh spearmen. And knights do seem to have been the dominant arm in most medieval battles. The basic militia spearmen should be just filler units - they perform that role fairly well (ie are pretty bad) already in M2TW.

BUT, if you get a well armoured knight who has trained for combat all his life and stick him on the ground with a bunch of fellow stout hearted men, the story changes. My money then would be on such foot to be able to beat off their mounted counterparts. That's why the French knights started fighting dismounted in the Hundred Years Wars - they could not run down the English dismounted knights and, no, it was not the longbowmen that stopped them doing so.

Unfortunately, a lot of this is messed up in the Total War system thanks to the arbitrary and ahistorical sword vs spear unit distinction. Dismounted English and French men-at-arms often used lances (cut down or not) - ie spears - but we don't really have such top of the range spear-armed units in the game. And, of course, they would probably have mini-arsenals of poleaxes, swords, maces, daggers etc for when the fighting got up close and personal. I guess we have the DEK and the billmen as compensation, but currently, they are useless against cav.

Total war does have some intermediate spear units - the Italian militias, armoured sergeants etc. I see them stopping mounted knights due to decent morale and numbers. It would probably degenerate into a bit of a shoving match, as at Courtrai, but in the end my money would be on the foot if they were attacked frontally. M2TW has the balance here wrong, IMO. Mercenary spearmen and the like die too much to cavalry charges thanks to the shield bug or whatever. MTW/VI ended up with the balance between spears and knights about right, IMO: negate the cavalry charge, then allow slow, mutually assured destruction. The spears were a bit too strong against heavy cav in STW and MTW 1.0, IMO, although I gather the MP folk liked them that way for "balance".