OpFor: 2x Bullshark (60m total)
And utterly bullying them both with 4x Firestarters (FS9-H), which constantly cause the assault mechs to overheat and shut down, missing a turn. Also the AI wants to constantly put them in Guard mode to drain heat.
Use Jumpjets to get behind them and penetrate their rear armor. By the time you've done that, their structure should already be weakoned by the heat.