Originally Posted by
Nyanmaru
While the input about lower levels is appreciated (and interesting to read) it's like you guessed, it doesn't really apply to higher levels. Low level PvP (read as "levels beyond old level cap") was kinda broken since patch 2.0 was introduced. During TBC it wasn't as bad as it was starting with WotLK and onwards, all the talent overhauls mainly targeted endgame and made lower levels stupidly borked.
But your last point still holds true: Death Siphon may not provide as much burst healing or healing over time as the other 2, but it's the only talent that offers a (mild) DpS aspect. Biggest downside to this is that you are reliant on it's ability to deal damage to the enemy, if your enemy has defensive cooldowns up or is out of line of sight, your healing possibilities are severely lacking. And makes it unreliable from a survivability point of view.