So I just gained a single seventh level spell for my mystic theruge, and I was looking at one of these spells to be my spell known. My biggest stat is in wisdom (28) and my chrisma is secondary (17), which is why I'm debating the two rather than just taking waves of ecstacy.
Any opinions would be nice, or perhaps something else, if you think that it would be better!
One round of stun on a failed save is a game-changer. But it means you'd have to reliably get it to work on your targets...who will be rather close. Stagger for one round on a save isn't bad...but at 30', foes could still close with you potentially. And casters will just use their own magic without worrying about moving.
Exhaustion has serious effects on ability scores key to martials. Not to mention screwing with movement and targeting one of their weaker saves. Again, you'll be relatively close when you use it.
Waves of Exhaustion is one of my favorite high lvl spells. AoE No Save -6Str/Dex, half-movement speed, and you can't run or charge.
That's nasty even for non-martials.