Grenades...

Endgame, you only need:

*a stack of medkits,

*a stack of batteries,

*a phoenix kit,

*3 to 5 stacks of ammo (that's about 240 to 400 ammo EXTRA ammo on top of what's currently in your weapons, if you need more you just suck at aiming or you're dual wielding LMGs),

*maybe a stack of cells for quick in-the-middle-of-fight shield healings

So in total, between 7 to 9 slots are taken.

If you have a blue backpack, you can have 12 slots in total. That means you can have between 3 to 5 slots open to carry grenades - > 6 to 10 nades total possibly. 
If you have a purple or golden backpack, it's ridiculous as you can have 14 slots total. That means you can have 5 to 7 open slots to fill with nades -> 10 to 14 nades total possibly. 

Even if you give or take 1 or 2 slots for other things (like weapon upgrades or syringes), that's still 4 to 8 nades for blue or 8 to 12 nades for a purple backpack. Now multiple that by 3 players in each squad. Yes... The nade spam can be quite real and disgustin. Also, a couple of times where I was the only person alive in my squad I did manage to disgustingly win the game with pure nade spam (given the enemy squad had to be grouped but still...). Also, barely anybody uses incendiary grenades and everybody uses arc stars as they are so much better.

To fix the nade spam and to give more incentive to use different nade types they need, imo, to give grenades slots just for them and reduce the total slots of items from 14 total to 12. Each grenade types can have 1 total (1 inc, 1 stars and 1 frags) carried at once by the player and those nades go in a special "pocket" that isn't tied to your inventory size. This will liberate slots so people should now be able to carry multiple scopes. To go along with this, they need to implement a way to (on the fly/at the press of a button) quickly rotate between available scopes for the weapon currently being held.