I took them out for my stealth rock/spikes guy
and Gliscor, because i've seen it stall better, i wanted to try a stall team also and dragons =P
And even your chancey outsped my Dragon Tails, (-6 priority move) with my speed at like 328, chansey with max 282? thats 40 speed higher, +6, I guess priority + beats speed +
Also, Hydreigon and Haxorus don't get Roost. or any recover moves.