Mirc
Not mIRC!!!
It's a relative issue, really. At the time Cossacks are available, the highest attack unit is 6. So there's not really a unit that's a whole lot better offensively than that. It would be like calling a Tank a good offensive unit because it's defensive rating his higher than all the rest of the attack units (save the tank, of course) around them. It's still an offensive unit, just being used (incorrectly, IMO) in a defensive role.
Also, calling an apple an orange doesn't make it an orange.
One word: Sipahies.