I'm thinking the Prime is a dedicated Battle Armor carrier. All armament in the arms, no hands so arms aren't particularly active and unlikely to brush off BA accidentally (implicitly an occasional issue in the fluff, per Fire Moth fluff), long-range weapons to provide covering fire for BA.
Since BA and vehicles don't as a general rule follow zell like 'Mechs do (nor do 'Mechs follow it against non-'Mech targets), the Gargoyle Prime can carry BA and then cover them while they destroy enemy vehicles and BA. Plus, if we take various TacOps rules and assume they represent greater realism, LB-X ACs are sorta good vs Battle Armor because all hits have chance of instantly incapacitating a trooper.
Naturally this still leaves the Prime weak in standard BT games, but i do think it has a role in-universe, and reasonably common at that.
The Gargoyle's brother, the Timber Wolf (both descend from the Woodsman) isn't as suited for BA carrying due to it nearly always mounting heavy weapons in torsos, plus in general its shape may be less suitable for BA carrying even though this isn't modeled in the rules.
Further, assuming the most difficult tech for the Clan to produce is Endo-steel, the Gargoyle may be more practical for the Clan Wolf to produce than the Timber Wolf, despite its greater mass and higher rated engine. Indeed, didn't the Gargoyle become relatively widespread whereas the Wolves defend the Timber Wolf is exclusively manufactured by the Wolves? (The Gargoyle is a decoy and a consolidation prize.)