Hybrids are almost never 'completely' bad in 1 season in the same way that pure classes can be, they almost always have other options.
And since we were talking about classes, it doesn't mean shit if you as a healer don't want to play a DPS, it's still the same class.
Sorry I kept the list short because I incorrectly assumed when I said "and so on", you would understand the rest.
Warlocks switching between destro, affliction and some demo, rogues switching between sub and mutilate, mages switching between frost and fire, occasional arcane.
Let me try again, you can not compare arena viability of 2 classes when 1 can fill 3 roles(melee, caster, healer) where as the other one can only be one type of dps. Especially when viability requires transition between dps and healer. Your "class" becomes something entirely different due to the fact that healer skillset and dps skill set are completely different, where as dps class changing spec has the same ROLE.
I don't play dps and If I wanted to play dps, I would roll one. So no, if my healing specs become not viable, there is no option for me, i.e "no big deal if disc sucks go shadow", to me that's equivalent to "my class is bad"
That's why you can't generalize all specs of hybrid classes.