exactly. the game your playing is nothing at all like the game at 70. the game at 70 warlocks are kings of the attrition playstyle. they embody the "i get stronger as you get weaker" playstyle. a popular counter to warlocks is to target their pet; the fel hunter is the most popular arena pet, and for good reason. for a rogue or a warrior, killing a fel hunter isnt a problem. killing a voidwalker is a much harder proposition, and many warlocks know this, and will adjust their strategy accordingly.
i hate to pull "rating rank", but i have played at the 2k+ level in 2v2 and 3v3, as well as the 1800+ level in 5v5. this is less of an issue in 5v5, but in 2v2 and 3v3, as well as pvp in general, a drain lock with good pvp gear is something no one can kill easily, or without significant help. even skilled and geared rogues need help, and they have a much easier time of it than any warrior will.
MS affecting drain/siphon is a needed thing. not only for balance purposes, but simply because they ARE heals, despite what many hair-splitting opponents will say.