PLA must develop 12.7mm variant too. As it's smaller in size compared to the 30mm ammo ... thereforeo more ammo to shoot down inexpensive drones !
More (smaller) ammo doesn't mean better mission capability.
12.7mm needs hit-to-kill whereas a larger round allows for more sophisticated capabilities such as pre-frag and airburst - with these, close enough is good enough. Which may translate to less rounds required to achieve effect - much like the way PGMs have reduced the amt of ordnance required by an order of magnitude or more.
To give an example of how smaller doesn't equal lighter in this case,
Ballpark, a GAU-19 spits out about 20rnds a second. That's about 3.5kg of 0.5cal ammo a second. Say an engagement is 3s, that's 10kgs of ammo. (Consider most C-Ram systems with 3x the RoF do take about 3s per engagement)
A 30~35mm proximity fuzed round is about .7kg a round. Ballpark 5~10 rounds per engagement and you're still looking at 7kgs vs 10.5kgs. Smaller (lighter) bullets ends up costing you 50% more ammo weight per engagement.
Fringe benefit of a SHORAD with a med-calibre gun with prox-frag ammo, it can function as a CRAM in a pinch.