It's the combo of high EMP, equally high mobility, and Diable's generally narrow shield arcs, also. (A tip for the new players; the Resistant Flux Conduits hullmod cuts EMP damage taken by half.)
My experience over the years has been that Diable's current fighter bay setup tends towards a very fine line between just enough and too much fighter; because Wanzers are so powerful and effective, and Diable's fighter doctrine is to disperse bays through out the fleet, once Wanzers hit a certain point they're impossible to kill off (since the more fighters you have, the harder it is to stress the replacement rate, and you don't remove that many bays with any given ship kill), so they benefit more from that snowball effect.
So I would say invest more in tanky low-tech ships with effective fighter defense (Enforcers with Flak/Dual Flak or Thumpers, and Heavy Armor) when you fight against them, and when you're using them... well, fighters are strong right now. But for more of a challenge, run a fighter-light or smaller fleet.