I took over mid-game as GM for a group of characters that are close to maxing out their advancements. Basically, any time they roll, it's a +5 (some move lets them use a +3 stat, and 2 others help them); we had multiple snake-eyes rolls that still turned into the 7-9 level of success.
Accordingly, I didn't get to inflict Harm and nasty custom moves the way I would have liked, and I got worried for a bit that my creepy maelstrom constructs would turn into a hand-wavy cakewalk.
I was also a bit creatively strained trying to expose helpers to fire/danger/cost when they played their helping as merely giving verbal advice to the primary acting character.
But! It was still a totally fun session. A distant buzzing sound from deep in the jungle is still scary, even if you kick the giant dragonflies' asses once they arrive. "Friendly help" on your equipment from an unknown agent is still ominous even if there's no problem to be dealt with yet. NPCs ranting about powerful folks who've forced them to do things still casts a shadow, even if these powerful folks are toast if the PCs ever find them.
(Oh, and indirect costs are always fun too. Nothing like offhandedly killing a longtime NPC to give a mismatched fight some consequence. Yay "looking through crosshairs"!)
To me it seems less a question of whether the PCs will achieve their aims, and more a question of how and in what order and whether they'll change their minds. So I'm planning to make those decisions as interesting as I can. I think we've got some good momentum toward a "The nasty things that live in the psychic maelstrom are people too!" quandary. Just imagine Agent Smith as an adorable child.
For anyone who's read Ex Machina, I'm modeling my maelstrom critters on the dimensional openers. Needed to tone down the White, but the Green is some serious shit.