1 "shot" from AGL isn't 1 grenade (I seriously doubt one 30mm grenade would have the same "boom" as an 81mm mortar round
), same way as with autocannons.
And ccrew of 3 serves to give the mobility and atleast some ammo. How many of the 29-round drums is a gunner able to carry along with the AGL? How many the assistant with tripod? Same way why MMGs have a crew of 3.
Besides most TO+E I've seen rate AGL squad (Russian) with 7 people: Squad leader and two AGL teams, each with 1 AGL and gunner, asst. gunner and ammo bearer.
Of course if you have better info (after all you do not have the language barrier) I'm all ears