Another interesting option with drains, and one that I haven't had the opportunity to crunch the numbers on just yet so not sure of the validity of it, would be to have both the debuff and the buff portion of the drains be percentage based. Meaning that even if you are able to cast the top drains at level 20 you would get more benefit from it at level 220 since both you and your target would be more effected with a higher base skill. Again like I've said I've not crunched the numbers so no clue how this would actually pan out in a real life scenario but its at least something to bounce around.