Elves excepted, Pridemage is just better if you have access to :w:. Sage has the advantage of a 2-for-1 like you said, but it's usually outweighed by Pridemage's advantages. Namely, blowing stuff up at instant speed, GSZing for one less mana, and being able to fetch it and beat with it until you need its ability instead of having to wait until the troublesome artifact/enchantment appears.
It's obviously not a bad card, and I'm sure one can encounter times when Sage's 2-for-1 matters more than Pridemage's strengths, but I firmly believe those times to be strongly in the minority.
Harmonic Sliver existed for years and was mostly viewed as inferior to Pridemage. Sure, it's different from Sage by having 1 power, requiring :w:, and carrying the risk that Sage doesn't have of blowing up your own artifact/enchantment if the opponent has none, but I think it's a suitable analogy.
Pridemage hitting for 3, not having 1 toughness, and granting Exalted goes a way to negate Sage's 2-for-1 bonus point, too.