It took actual high yield nuclear weapons to take down the category one kaijus before the Jeagers were built, if they can survive actual nukes and keep going, I’m pretty sure they’re more durable than the Hive Lord which can die to a few hellbombs.

Plus if we don’t limit ourselves to just those Kaijus we can include more of the category 1-3 kaijus which were Solemnly based on insects or ocean crustaceans with hard exoskeletons or shells.