Tech tree issues.

[Ahriman]

Yes, in reality, any decent weapon requires metal.
But as I've stated elsewhere, I don't think a metal mine signifies the only "access" to the metal (copper and iron are very common), rather it signifies a metal source and manufacturey of particularly high quality. So, to make knights you might need the iron resource because you need good quality weapons to equip and maintain large quantities of knights. Similarly for advanced pikemen and the like in heavy armor.
But Longbows or Crossbows only require tiny amounts of metal for arrowheads and construction relative to that in outfitting armored knights, and need not be of particularly high quality. The real important inputs are in the bow-crafting and unit training (hence bowyers buildings and archery ranges give bonuses).

Oh and yeah, the Mongols were able to take many cities without a fight... because they had such a big army relative to defenders that most defenders could see that resistance was futile and so would surrender.

 

[Adrogans]

Okay, ya got me. I agree with the archer thing they do require very little metal per se. i just wanted to point out the whole testing thing they did (was to find out if the english longbow was actually useful at Agencourt and they found that the Longbow was actually ineffective against the knights and that the lack of armor was actually the winner due to the extremely muddy conditions the day of the battle causing the knights to get stuck and lose mobility and the smart use of terrain)

 

[Ahriman]

Yes, most archery casualties aren't from punching through solid armor, they're from arrows finding the gaps and weak spots. And put enough flying metal in the air, and some of it will do just that.

 

[Adrogans]

Naw, they had few archery casualties, they think based on the descriptions and test that the mostly low class archer soldiers simply walked around and slit throats since the knights couldn't move and the commoners didn't obey the whole capture and ransom thing attitude. It was actually an awsome show on discovery channel.