It doesn't. I did a review of the product, and their expansions, on my blog. I used WW II as the playtest also. Basically I set Behemoths as King Tigers to get a differentiator, but otherwise there was none between a Sherman and a Panther; they were both Armor.
Whether that works or not depends upon the scale that you play at. If you imagine each vehicle model is a single vehicle, then you are not going to like it all that much. If you look upon it as a platoon or so, then you can start to "justify" in your mind that the Sherman model is a reinforced platoon – and counts as Armor – while the Panther model is an understrength platoon low on ammo – and also counts as Armor.
The expansions do add differentiators. And once you buy one you get the idea of where the designer is going with it. In a way, it is like Saga. For every advantage you need a disadvantage to even out the point cost. Either that or you need to come up with a comprehensive points system to make things "fair". Maybe the best idea of all is to simply rate effectiveness of each weapon system, historically, then play a historical scenario, points be damned.
Modifying the game is easy. If you think a Panther should hit harder than a Sherman in the game, simply state that the Panther models are up one step against the Sherman. If you use lots of different tank types, make a list of what beats what. Or assign values. All very easy to add within the framework of the game.
I suggest you get the Technology expansion – at least one of them – and see how the author adds in a little flavor to mix things up. Stay away from the Experience expansion, it is a complete rip-off as it is not well thought out, and completely wrecks the points system.
Remember, TA:CC is basically HOTT for WW II and Modern, so it intentionally generalizes values, just like HOTT. The idea is to give a fast game. I think it does not succeed in that last part, however, because the end game can get tedious trying to eliminate units that are out of action. (Out of action elements are not vulnerable enough to elimination, in my opinion.)
