Can't get serperior till pokebank comes out..
but yeah, don't use solarbeam, even in sun. Contrary leaf storm is the best grass move you could possibly have with serperior. solar beam is just no. especially when leaf storm has higher power and can only make you stronger with contrary.
In that vein, Giga Drain is just no- do you want it to die? They're not gonna give you something weak and juicy to suck up with giga drain before they toss a fire or ice type your way to deal with it first. If you're lucky in x/y, the hidden power is rock, so use that. Other than that... use toxic or swagger against those pokes that want to sucker punch you. You can use safeguard to foil thunderwaves that would foil your sweep or use reflect / lightscreen to allow it and its team to survive more.
And don't listen to the absol much. You can max spd and spA and allow the contrary to boost it into sweeping. or you can gamble on contrary and either some def or spD to let you tank through an attack or while while contrary beefs you up (still max spd for sweeping). I recommend max spA and spd to outspeed as much as you can and get max benefit from its attacks. I used to spread EVs about kind of evenly too, but really the best things to do in meta is power up areas where they're already strong (like a glass cannon for sweeps) or shore up weak defenses of any sort/hp to give tanks/stall longer survivability.