I am of the opinion that grenades are clumsy to use: you have to holster you weapon, take out the grenade, take out the pin, throw it and re-equip your arm. Every step includes a painfully slow animation and leaves the operator vulnerable for quite a long time.
This problem is made even worse with the C4 and IED and the flash bang. With C4 and IED after throwing the explosive you have to equip the detonator. This is of course automatically done except when you equip your weapon mid-throw to throw longer and to be able to fight earlier. In this case you need to scroll through the carried grenades because the detonator jumps to the end of the list.
I think the detonator should take the slot of the thrown explosive and be faster to equip.
The flash is meant for quick action. In its current state it is not well-suited for that, however. The flash could have a special animation where the operator throws it one-handed. If this turns out to be over powered, it could be restricted for the breacher class only.
These problems could be solved without any re-works by implementing the ability to choose different presets of keybinds for the classes. The number four is currently taken up from every class by the commander's binoculars. There are very little free easily accessible keys left so for example freeing the 4 key from the binoculars and G key from the bi-pod as breacher for grenade binds would remove a lot of frustrating elements from the game.