What makes you think that? It's still an offensive dispel, without a cd. Over the course of the past 2 expansions however, it was first reduced to only dispelling 1 buff, then back to 2, and a few patches ago back to 1. There is now a glyph however which makes it a 6s cd but dispels 2 effects (which is useful when you play for example with a shadow priest, i.e. when you are not the only one with an offensive dispel, to save a global).
In PvE you generally want a mage to spell steal the buff instead of purging.
In PvP it is highly useful to dispel powerful shields/protections and even regular buffs - removing a PW:Shield, some Damage Reduction or a Fortitude buff can weaken a player more than any other spell in our arsenal.