Yes zen raped me on cat with beast, but oc can't be beaten on crucible, the centre jumping is too epic, lets you dominate flags and with so much splash dmg, you can dominate exp as well without actually being in the creep waves, whereas the beast has to be in there to kill them, and he has to waste time walking back, or use tele scrolls to go to crystal. You don't need tele scrolls very often, this saves money. if you are using the uberfix you can negate 1 spit every 20 seconds, plus 2-3 seconds of the previous spit. Minions are good against beast. And once you get exploding ballz, thats very nice too. Also the permanent mana/helath regen freeze on the beast is good too. also, since theres only one portal on each side and all the reinforcements go through the centre, oc can hold them off very well.
As for sedna vs oc, she'd have to get cloak of night to centre jump, while oc is free to have blood or something. Heal is nice, but sedna wont have much actual damage, as her minions will be dead, and ocs wont be. She may not be able to be killed if played correctly, but her splash dmg is severly lacking, and oc should be able to push with reinforcements without much trouble.
In case its not obvious why oc isn't as good on cat, theres no centre jumping, and theres more than one lane. Making the experience and flag domination much harder. Also since theres more than one lane, he cant defend them all at the same time, until the creeps reach the middle, and by then giants are a handful for any single dg to stop. There is 2x as many creeps on cat, harder to deal with, and of course theres 4 portals instead of two, making it more difficult to defend all of them. You have to mess up pretty bad to lose your portal on crucible, whereas on cat, you can't lock both of yours.