Two reputable folks have recently made statements which I find quite disturbing:

Quote Originally Posted by mad cat mech
pikes are at their best if given the weapon upgrade. this adds 6 attack and gives them the chance to inflict massive casualties at start of melee before an enemy bust through the spearwall.
Quote Originally Posted by Lusted
Weapon upgrades give a +6 bonus to attack despite only shwing +1 in the unit stats.

Armour upgrades give a +2/2.5 bonus to armour despite only showing +1 in the unit stats.
References:
https://forums.totalwar.org/vb/showp...1&postcount=12
http://www.twcenter.net/forums/showp...15&postcount=3

If they are both correct (and it's safe to say they are), then factions with fortress or large city-level swordsmen would get a HUGE advantage over the other factions.

For starters, let's compare Mailed Knights with Mamluks. Their stats are fairly similar except that Mamluks have an AP secondary attack. Thus, with no upgrades Mamluks are superior to Mailed Knights.

But imagine what happens when Mailed Knights get a weapons upgrade. Their charge is now a whopping 22. Their attack is at an astounding 16. All it took was ~30 turns of getting a fortress and ~15 turns of building DFK's. And now Mailed Knights are head-over-shoulders better than Mamluks.

How can the Egyptians possibly compensate? They can't.

They can get a Horsebreeder's Master's Guild very early in Cairo, but one measly experience point can't beat +6 attack. They can upgrade Mamluks to heavy splint, but that requires a Citadel-level smithy and still can't compare to +6 attack.

Basically my point is that +6 attack for a weapons upgrade is ridiculous. Either some CA developer was inebriated when he chose the bonus, or there is some extreme favoritism towards swordsmen.