Global upgrades are about economical decision making.
If the upgrade is so bad that no one gets it, or just a handful of people do, it needs changes.
No one ever got zookas, so they got merged with BARs.
Now no one ever gets zookas, but you have them unlocked at least.
Global upgrades are good idea when they are actually USEFUL.
Having upgrades for the sake of upgrades is horrible design.
I did use zooka pre-nerfed, on RE I think it is decent.
I think the dev merging the upgrade just to match the Brit standard, not because it is useless.