I don't know very much about how the services develop and procure new small arms, but I can't imagine entire new weapons (like a new LMG or HMG) are developed or procured at only the brigade or even group army level. I can imagine certain brigades and/or group armies will receive priority for new small arms but actually requesting new designs seems like it would be done higher up.
But then again we've seen quite a bit of inconsistency in the PLA with different units sometimes having different variations of weapons and/or accessories that we don't ever see again in other units so who knows.
We've seen different PLA units receiving what seems to be personalized & highly-customized gear, so it is definitely possible that some procurement decisions are made at such levels of command. It makes sense too, since different units face varying conditions & operational requirements.
If enough troops and/or commanders voice a common concern regarding a certain aspect of their equipment, that request is usually heard at the top; this is common to almost all professional & organized militaries.
