Didn't it already get buffed to 300 because it was too low before?

400 would make it virtually just as good as the melee combo (the 1-2-3 combo avg's 410 potency per 2.2s) so I suppose it's still a loss once you factor in Holy/Flare and Scorch, but it still seems like too much given how little Mana you're spending.
If someone could math it out over the course of a fight, or maybe over 2/3 minutes, to see if just spamming Enchanted Reprise a couple times every third and fourth GCD between spell combos turned out better than touching the 1-2-3 combo, I wouldn't be surprised if 400 put it in the lead.

It's not meant to be a part of your rotation, it's a gauge spender to be used sporadically for when you need to bring your Mana down to prevent capping.