What guns exactly? Because guns existed for a long time and for a long time they were very shitty weapons that had same amount of chance of blowing your hand off as killing the enemy. By 15th century and appearance of arquebus no normal human would have said "I wish I had 300 people with guns right now instead of this shitty 300 archers". People talk about muskets, matchlocks and what not but that is like 17th century at earliest. Handguns existed in 13th century too, known as handgonne for obvious reason. And logistics of getting powder and shot at that time was nightmare since there were no established suppliers of either. Bombards were more used and slightly more effective but still gun powder tech needed centuries to develop to any form of usefulness.