Have you considered Choice Scarfed Salamence in place of Haxorus? I have used it a bunch of times and it works great, but Gensect can take advantage of you being locked on Outrage because he can wall it. But keep in mind that Salamence can out speed Gensect with Choice Scarf. Or maybe Landorus (which might seem stupid in rain) if you are having trouble with steel types. It also works awesome against T-tar and Ninetales. I hope I wasn't dumb and able to help.
Salamence @Choice Scarf
Evs: 252 Atk / 4 SpAtk / 252 Spe
- Dragon Claw
- Fire Blast / Brick Break / Hydro Pump (Egg move) / Aqua Tail
Fire Blat will always OHKO Gensect and 2OHKO under rain. If rain is up and you play your cards right you can predict a switch in and 2OHKO since you out speed. You can also use badass water moves like Hydro Pump or Aqua Tail if you can't deal with Gliscor. But keep in mind they do carry Protect which might make it harder to take them out if you're locked on a water move.
Landorus @Life Orb
Ability: Sheer Force
Evs: 252 SpAtk / 4 SpD / 252 Spe
Modest (OHKO's Gensect)/Timid Nature
- Earth Power
- Focus Blast
- Hidden Power Ice
- Rock Polish / Substitute
This guy can easily get rid of steel-types especially Gensect. But problem is he can't take him out without Life Orb. Since Gensect out speeds you can set up a Sub crush him when he comes in. I am not sure if Rock Polish allows you to out speed Scarfed Gensect but it might. He is kinda hard to use in rain because I really can't fit him in my own rain team but in case you might like him I put him there.