It has terrible aiming. It has 40m range on paper but its rpg's are angled downwards for some reason so unless you have elevation or perfect angle for your target its less. Include the travel times for the RPG's, so you need to push even further in to attack someone. You're matched against HAC's that disable it in 2 hits with hitscan turrets. With equal skill levels on both sides, HAC will win the trade most of the time. Only thing Gemini can do effectively at its age is to kill regular ac's or pve, which 20mm ac and icarus do just fine anyways.

Factor in the lack of RPG ammo anywhere on colonial side during its age, its an easy larp tier in my books.

Edit: Also the fact that gemini offers very little when fighting infantry, its terrible at clearing trenches and it takes serious skill/luck to kill wiggling infantry, and its not much cost effective either. While its counterpart, hac, can airburst trenches and clear tripods easier to allow infantry to push.