Any article like this will always skew towards modern players. He at least makes an attempt to put in deserving QBs from past eras. You can definitely put older QBs in the discussion. The problem is that people just look at stats and think that they know the story.
My rankings for top 5:
1. Graham
2. Brady (I usually do not rate players before they retire, but I make an exception here)
3. Unitas
4. Baugh
5. Montana
Baugh and Montana are relatively interchangeable. Using strictly QB play, Montana. However, you need to look at the totality of the player's contributions on the field. Baugh takes it over Montana.