Since Patch 1.2 I found it quite a bit easier to beat the aztecs, even with armoured swordsmen and the likes. Just remember to bring more than one army, two or three full stacks should do the trick. Oh and I think artillery and ranged units can be very effective, the Aztecs like to start with a ranged duel after which my arquebusiers and cannons have sometimes wiped out half their army or more. When they then charge my infantry, they're easily routed by a few cavalry units on the flanks or in their back. Making sure your units have armour and especially weapon upgrades also helps a lot.