It is not dispellable. And gl soft cc'ing your target with polymorph or anything like that on battlegrounds. Whole bunch of cavemen playing alongside you are just waiting to break your cc.
Anyway, why do we have to compare what is more op, shmourne or faps? Do you realise shmourne wielders can also use faps? Do you know how op are they when they do?
Do you even have an idea that shmourne alone doesn't make such difference as you try to describe it? Yes, it is bis weapon, but if you have best gear on every other slot, and have other 284 ilvl weapon the difference won't be that big. Not too long ago we had rank 1 arms/hpal with Glorenzelg. It's the whole scalling and pve offset items that make plate classes so overpowered. And now let's guess, what is harder to do: rewrite whole class balancing from scratch, making it 100% custom wotlk server, or just nerfing one small potion on bgs?