I don't play any more so I can't speak about the drop rates any more, but as far as the disabled spells go, they are disabled so as to allow the dev(s) time to figure out why they're broken and attempt to fix them. I seem to remember something about Chain Lightning having a retarded jump range on the lightning or something along those lines.
The channeled spells and DoT's are broken due to how haste affects them. Since the haste is just under max, channeled spells are near instant and don't do anywhere near their intended damage. DoT's also do damage more quickly (a retail thing, not just a server thing) based on your haste, so like the channeled spells, they only tick once, sometimes twice if you're lucky. I believe it would take some reworking of the haste scripts to fix that, so I doubt it will be done for a while.