The call in design is a balance issue; not the Greyhound itself.
it doesnt matter if its a call in or a built unit, anything from a 222 up pretty well will punish you for crewing a weapon with zero nearby support. thats the role of these units. if you have AT and a snare (that one is most important) the unit will be drastically less effective and exploiting you.
without a replay i cant give more direct advice but if you have nothing to stop a LV from cruising up to your team weapons and plinking away at them they will cruise up to your team weapons and plink away at them. its not a design issue, its not a balance issue, its called how the game works.