Balancing one of the most OP things in the game, without ruining the core of it

A quite vastly imbalanced part of the game, is the Support class' access to infinite healing and infinite ammo, but not the notion of the supply bag itself (even if it should be split into two individual bags, one for ammo and one for healing so it's a conscious choice what you bring like in BF4, but that's a topic for another day), but the imbalanced thing is the Support class' ability to have it be infinite for themselves, allowing them to be the most imbalanced class in the game by far.

My solution instead is as simple as this; Make the Support class not able to gain direct ammo or healing from their own bag (minus the mechanic for the mortar of more rapid shell feeding), forcing them to play more as a team instead of the lone-wolfing camping that has become a mainstay of the class in BF6.
That being said, it should still be possible to resupply yourself with the supply pouch as it currently functions, as it is limited and has to be restocked before it can be used again when you use up all the charges. This would promote more use of the supply pouch as well, and fundamentally balance the class at its core by eliminating its "one-man-army" flaw.

This would also promote more classes being used and using their respective Signature Weapons more frequently, rather than any weapon in the game being only played with Support to level up the weapon, due to the infinite ammo being the "go-to" for such, as well as after all unlocks and masteries are done for the weapon.

There are quite a lot of the things with the Class Signature Sets that need addressing, and there are definitely enough complaints about the Assault class' Gadget 1, but this would be a first step in addressing one of the most imbalanced things (if not THE most imbalanced thing overall) in the game.