The Aztec culture has always fascinated me, yet I cant figure out how they hadn't developed weapons on par with the Columbian era. Is this because they were completely isolated from Western Europe/Asia?
I'm not asking how they fell. Disease did a number on them and it's impossible to combat against an army armed with horses and advanced metallic weaponry. Also to my understanding there was a lot of infighting within the Aztec world, and a rival tribe (the tlaxcallans?) even helped Cortes conquer Tenochitlan.
You're assuming linear progression of technology. Technology is adaptive to local requirements.
The Aztecs weren't "hundreds of years behind" the Spanish. They were well-adapted for their own environment and sphere of influence, with interesting techniques such as nixtamalization. If you're predicating human progress purely on weapons development, keep in mind that the Aztecs/Mexica were already successful within their sphere.
Keep in mind also that "different" does not mean "inferior". The Aztecs developed differently. That doesn't imply inferiority, or that they were behind the Spanish.
This is a very popular question, and it has a whole section to itself in the FAQs.
There's always more to be said, but I think those threads are quite comprehensive. Particularly this one with /u/The_Alaskan and /u/anthropology_nerd and this one with /u/RioAbajo.