I've used them to great extent in a 400 point team epic tournament (almost the best time I've had in X-wing). I believe they were all running predator? and Ion Cannons. Despite having the misfortune of coming up against quad IGs and an ungodly 8 Falcon heavy swarm, they really pulled their weight. The trouble is that Gunboats do everything better.
For the price of a predator and Ion Glaive with MKIIs, plus three points, you could run two Ion cannon gunboats. Heck, for a meagre 28 you get a HLC boat, which is going to do more damage than the ion, primary and ruthlessness combined. They've just been outdated in a format where token stacks are meaningless.
If you want Defenders, then 6-8 naked X7 Deltas are the way to go, probably paired with some AOE munitions from gunboats and a small bid (3-4 points should do it). If you can squeeze in howlrunner and a way to keep her alive, all the better. The sheer hull and shield pool, combined with unblockable token stacks and howl rerolls, should melt just about anything before it dies down itself.
