I saw the preview versions of the Archmage and the Heirophant when they were released online and both of the classes were pretty much identical - you sacrificed spellcaster levels for neat metamagical powers.
In the game we were playing at the time, we used those versions (nobody had gthe FRCS) and the Archmage was really, really nasty.
When we switched, he was just BS. Sacrificing spell slots really means very little compared to the sheer level of power you get out of the high arcana.
So yeah, compared to the Archmage in 3.5, the Heirophant blows. Either house rule the Heirophant to keep getting caster levels or fix the Archmage to not be so ridiculous.