well, I know there's already someone submit a bug report about mob drops. And this bug still hasn't been fix.
I know you guys said that mobs have a low chance to drop armor/tool...
I made a pillager/raid farm and a skeleton farm, none of them drop bow or crossbow, with looting 3. Also I made drowned farm and you know what, I get a lot of trident from that farm alone without using looting sword (from minecraft wiki, it said there's 11% chance of getting trident).
In skeleton and raid farm? I didn't get a single bow or crossbow (from minecraft wiki, it said there's 11% chance of getting bow from skeleton using looting 3 sword and 44% chance of getting crossbow from pillager using looting 3 sword)
I noticed this bug in 1.12 beta version and I though they're going to fix this bug, but I guess I am wrong then