For the way I play, the warrior-swordsman is a bid thing since it is expensive, but does give lots of kick to an offensive. The AI often doesn`t attack a 4 swordsmen stack, but will take bites off a 12 warrior one.
On the other hand, the inceased mobility of the Horse units makes Swordsmen rather pathetic..
Same goes for the Tank - Modern Armour thing: it depends a lot on playing style.