"Primary role", "secondary role" and the bars displaying a champion's attack power, defense power, and difficulty etc, are mostly there to help new players get an idea about a champion.
I doubt they are meant to be accurate for ranked games. For example it would be a bad idea not picking an ADC like Jinx and instead getting Teemo, just because he has a "Marksman" tag on him.
In normal games, players tend to try out new things and not trying hard, so Azir Marksman might work. (By marksman i mean a build focused mostly on your autoattacks.)
ADC Azir would still be a bad idea since nothing scales with his AD.
Your soldiers cause magic damage when "you" autoattack. Your total damage would be mostly magic. Therefor, your primary type of damage would be magic. That means that you must build AP items, and perhaps get some item that increases your attack speed as well. A good fit for that would be Nashors Tooth, since it gives you AP, attack speed and cooldown reduction (which further increases your attack speed because of his passive).