Darmanitan is a pretty big threat to this team, especially the scarfed variants. If Garchomp is gone, than it can mean hell for you. You may want to go Latias over Gengar, since Latias can provide Wish Support, which allows Chansey to swap wish for aromatherapy (which your team would love to have) not to mention it can survive Nuclear Flare Blitzes and kills washing Machines.
Garchomp also wants a Yache Berry, I've used SD Chomp in the past, and things have managed to pull HP Ice out of their ass and end my sweep.
I'm not sure exactly what the use for disable is, Gengar seems better off with Taunt.
I really think you ought to go Scarfchomp, though. You already have Gengar and Mienshao for Natt and Outrage murders any non scarf +0 Dragon, it even kills +1 Salamence.
Chansey is a better wall than Blissey, but access to moves like Flamethrower and the ability to not be completely walled by SubGhosts makes Blissey a better choice in OU, imo.