Frost is better at scaling infinitely but Gara heals stupidly well nowadays with a couple augments and can keep the defense objective alive very well, especially considering that build also has the augment for applying her splinter storm to everybody. I would consider her superior for all normal gameplay including Steel Path, as she can handle melee Eximus significantly better than Frost. If even one melee Eximus slips through the cracks, the defense objective is a goner with Frost.

In addition, you can build range on Gara and easily always have an enemy in range to be hit with mass vitrify. On top of that, splintering storm protects against melee units and her 3 will taunt enemies into walking into the center (like say, where a defense objective is with a highly-damaging splintering storm). While an enemy being passed over by mass vitrify does mean that enemy is now inside the defensive ring, her 3 is an extra layer of protection that still works on Eximus and the enemy is slowed by mass vitrify’s touch anyway.

In my opinion, Gara is easily superior at defense than Frost at any level, but that’s harder to argue so I’ll easily settle for anywhere outside endurance.