That’s… new to me. I’ve killed Haderax at least 100 times and I’ve literally never, not one single time, seen a legendary grenade mod in the boxes (he has dropped the occasional Fire Bee or whatever when I killed him).
For me, the boxes heavily favor Strikers, Hellfires, and Pitchforks. I’ve seen far more grenade mods, including Quasars, drop from Uranus. He just never drops the right one. I’ve got at least three 0.0 fuse time lobbed Quasars from him and one 0.0 fuse time Homing. Probably a rubberized too, which… yeah, no.
But what the hell; I’ve got nothing better to do. I’ll give it another shot with Haderax. At least he always drops level 80 gear, unlike Uranus and the UBA Varkid at the end of round 2 of Creature Slaughter.
EDIT: Been at it off and on for a few days and I’ve got a couple of Quasars (nothing good though), but an absurd amount of Pitchforks, Hellfires, Skullmashers, and Lyudas. I’d go so far as to say that Haderax is the best spot to farm Pitchforks (though I don’t know why anyone would want to do that).
He’ll have Conference Calls and Bitches with somewhat less frequency in the chests, but - noteworthy for people who’d want to farm Bitches - far, far, far more frequently than Bunker drops them. Which is nuts because they’re designated for Bunker, and just goes to show how poorly thought out his loot pool was. I’ve complained about Bunker elsewhere (as most people have), but I really want to say that Haderax is a better place to farm Bitches. Not good, but better.
Grenades? To be fair, I’ve seen more than the zero I’d seen before, but they’re usually Fastballs. I’ll keep going and hope I stop seeing pitchforks.