I think the Diable are a fairly balanced faction. The faction revolves around overwhelming fighter/mech firepower, and it does that niche extremely well.
Take it out of that niche, and it no longer becomes the powerhouse it is. The individual ships of the faction, the cruisers, destroyers, capitals, ect, are pretty easy to kill in my opinion.
The ships are far less tanky than Neutrino ships, and have far smaller shields than the Tri-Tachyons. I also feel that it has rather mediocre flux stats for a high tech faction.
All in all, load up on your PD, take out the mechs, and you should have no problem taking out the ships left behind.