The gyro isn't much of a problem, the engine is as the IS XL doesn't mix well with the concept of a Zombie Mech.
Use an armored Clan XL engine perhaps?
It's a Clan XL Engine, and armoring it would take a LOT more weight then armoring a Compact Gyro. I know the TRO does not show this, so it is not your fault for not realizing. The DHS are IS - not the engine. This makes it so you have to take out BOTH side torsos to really get it down, or take out a side Torso PLUS get a crit on the center - which is not going to be easy with Hardened Armor and Reinforced Structure. And like I said, I'd love to park a Purity near it. Would be fun seeing the opponent struggle to crack that nut.
Like an SRM Carrier parked right next to an LRM Carrier, and the enemy is like "Umm okay, what now?" But worse.
Things I'd consider:
Artillery. Maybe - though I mean the Mechs are not slow enough to die from anything but that massed, and massing artillery is not cheap and has problems on its own.
Battle Armor - though the Mechs could still maul that unless they are directly dropped. Even then, Purity can maul and escape and they will still likely die in droves from Turtle.
TSM Mellee + Talons! Pretty fun. Might work actually if used en masse. Or big TSM Quad Mechs using Mule Kicks!
Savannah Master spam! Pretty cool if we are just going by cost, or some cheap BV, though I mean, you are making a lot of lore breaking assumptions and logistical assumptions regarding Dropships and Jumpships. Like if SM spam worked in Battletech, no other unit would ever be used at all. The way I rationalize it is that Drop Ship and Jump Ship space is limited.
Nuke 'em from Orbit - That's the only way to be sure.
All of this also assumes zero support. I do play with making my own battle armor, aerospace, vees, etc. Just to complement this sort of stuff and making it even meaner, though in a pinch canon support units do wonders as well.
