Gara is similar but doesn’t do the same job. She’s a hybrid between Limbo and Frost in the regard that she offers damage reduction to both static and mobile targets while they give damage immunity to either static targets (Snow Globe) or mobile targets (Banish). The main difference is that Gara provides up to 50% DR to objects, whereas Snow Globe blocks everything.

In high level content, objects like Excavators don’t have enough HP to survive even a few hits from the enemies even with Gara’s DR and healing but Snow Globe can keep them alive by blocking the damage completely. There is Mass Vitrify, of course, but in order for it to work properly and have enough health, Gara has to hit multiple enemies while casting it. This means the enemies have to be close enough to her and hence to her defence target, which puts it at risk of getting destroyed before they get glassed.

Frost doesn’t have this risk factor which is why he’s better at defending.