Ran a few tests in the scenario editor, each one a few times. Level ground and melee units started just outside the range of ranged units. There are alot of factors but it gives you an idea. I used 5 units of each (15 total) for infantry vs. infantry. And 10 units(30 total) vs. 10 Calvarly.
Light Infantry vs. Heavy Infantry in Medieval: Heavy has 12/15 left
Light Infantry vs. Heavy Infantry in Gunpowder: Light has 9/15 left
The move to Arqubusier is, as we all know, BIG. I didn't realize it was that big though.
Then I tried a unit with it's counter one age ahead
10 Cataphracts (Classical) vs. 30 Crossbowmen(Medieval): Result? 7/10 Cataphract left. Conclusion: Counters are really fricking powerful even if back an age.
There was no focused fire in any of these I just let them have it. BTW, in any unit vs. same age counter it's usually no losses to the counter units at all except they take a slight hit once Industrial hits. There were 12/15 anti-tank rifles alive against 5 tanks. Hope this helps.