@KunstulaIt's not a bug. Here's the patch notes in which the weapon proficiencies were introduced: https://www.ea.com/en-gb/games/battlefield/battlefield-2042/news/battlefield-2042-update-notes-3-2-0 where you can see each proficiency outlined.
The reasoning is "speculation". It's what makes sense since support can drop both ammo and medkits, and is primarily focused on reviving. In BFV, the reviving class had SMGs. In BFH, BF4, BF3, the reviving class had assault rifles. Reviving classes shoot people around their subjects.
Ammo with LMGs isn't a balance problem, it's more of a boring problem.
