While i obviously don't have to the data that would be able to highlight how much, or little of an issue being a selfish player is. All i can go off is my in game experiences from BF6, previous games and beyond.
When you look at what things people have a tendency to take advantage over, it more often than not involves someone or something that provides for that induvial. The more this other person or object does, the more it's taken advantage of by the induvial if they are that way inclined. This is a sad truth.
So while yes, the supply pouch is an amazing gadget and provides a lot for the team when used correctly, it also provides just as much for an individual support player when in isolation. Which when the bag was split into an ammunition half for support and a healing half for medic there was less to take advantage of from one source.
With the supply pouch being an on demand heal and ammunition supply it enables the user to self for fill two needs. Utility they'd otherwise have to find at least one other player for. Which is too strong when in the hands of a competent player and is also perfect for someone who only cares about themselves or for individuals who might not be on the same skill level as other players, as they might not fully grasp the concept of teamwork and enjoy having a gadget that baby-sits and does that teamwork for them.
If they want to go about defining the individual roles of supports training paths further but want to keep support as one class. Do too little and it solves nothing with cementing the classes identity, you make them too individualistic from one another, ie fire support can no longer use the defibs and the supply pouch heals for less when using that training path. While this is a step in the right direction, but by which point you might as well make two separate more specialized classes with their own training paths, weapon proficiencies and ultimately clear identities and defining roles on the battlefield.
Thankyou for reading. :)