Me personally, never use fist of havoc on the ground. It WANTS to be used in the air due to the aftershocks it generates based on air time. It adds way too much consistency and power to not do it. Plus casting it in the air causes it to stop draining super energy until you hit the ground, which can save some time too.

I feel like FoH is not as bad, because the ability endlag is not as long as behemoth's. But I would still think it might be a nice "buff" without making it overpowered.

I generally agree with you, though I wish people would use it more in the air. I can't even begin to tell you how many times I've seen people ground slam and it does jack -blam!- lol.