I understand it is intended to push out garrisons, but is it actually meant to kill ALL the garrisoned units? That seems a little too strong. I think it would be better if the breach ability triggered a little more quickly, but only killed half the squad and forced them out of the building.
If previous tech and gameplay tests are any indicator, I'd say yeah, its supposed to be cinematic squad wipe, given how breach with flamer takes longer time then just flaming the squad inside to kill it.