A quick look at the real world shows that there's potential for far more than 100 meaningfully different weapons. Note that "weapon" does not have to mean "realistic modern military firearm". Don't discount the value of appropriately designed stat tweaks. If they tie into your game in a meaningful way then they can absolutely have a strong impact on player choice, actions, success and so on. For instance, you could have two different assault rifles which are basically the same aside from cosmetics and the type of damage they deal. If your game is designed so that different damage types matter then changing that one variable could make playing with those two guns significantly different. In other words, you can't look at this one thing in isolation.