Having given it some thought, I’m not entirely sure why we couldn’t have weapon pickups as part of the game. It could be quite interesting, and also be a good way to draw in players that expect it as a feature. There would need to be some limitations for certain characters of course and the entire system itself, but a lot of weapons would definitely be balanced alternatives for any character.
There are definitely some reasons why it could be very bad, but really only under certain conditions. Weapon pickups could diminish the FOPS role, heighten rambo play, reduce secondary weapon use, and possibly cause a class to suddenly become OP. All these things could be easily avoided though.
So why do I think weapon pickups would be a good idea? It’s quite possible to consistently achieve kill streaks of atleast 3 players with all weapons before a reload. Allowing for weapon pickups would allow an alternative to reloading and let a player continue their momentum. You could restrict certain weapon type pickups to specific characters. Picked up weapons could only have half a clip on pickup and require resupply for example, meaning that you might be able to pull off an extra kill per pickup if you landed every bullet. Pickup itself would have to be fairly fast, but could definitely involve a very short animation to allow an opponent to catch you off guard for an instant. The secondary weapon would still be very useful for situations where you couldn’t pickup a weapon, and even so might be a more reliable choice most times. I just see a well done weapon pickup mechanic making the game feel a bit more interesting and fast paced, and if implemented conservatively not hurting the game.