Simply put, both of these skills deal about +25% damage compared to a normal attack, for the cost of +50% extra AP. So they see very little use because they're not as good as saving or spending the extra AP on something else.
I have never used these skills all game. I don't expect that to change.
Even if you want to make the (BAD) argument that they're meant to be used as finishers if you only have 3 AP and can't do enough damage in one normal attack - which is a rare edge case, there's a problem:
The tooltip for Flurry says it does X damage 3 times, so for a player to decide whether Flurry is the right move to use to finish an enemy, they'll need to alt-tab out and open a calculator then calculate the new min and max damage for Flurry to see if that'll do enough damage. No one wants to do that. Flurry's tooltip should instead be changed to say "the total amount of damage from all three attacks will be X).
