The ease of using force strikes depends on your weapon, I feel. Staff's super easy, and wand usually is too. Blades and daggers, the latter especially, I've gotten pretty good at doing it in combos (specifically the dagger spin -> charging it while jumping back). But doing it out of nowhere can still be tricky, yeah; I feel like I need to get into a habit of a quick attack -> strike even when I need it quickly, since that's still better than fucking it up.
In relation to the challenge battle, the most frustrating thing with it is H. Edward's first skill. For some reason, he has some weird period of time at the end of the skill where he just like... stands there doing some super small animation, and you can't start the strike during it, so even attempting it makes it even harder to do once the animation ends as it'll read your hold as movement. Meanwhile there's that fucking skeleton standing there who just guarded the entire skill and is ready to attack you. I can't tell if it's intention is to punish you for not killing your target with it or what, but it's super frustrating.
I also think striking successfully when auto's on is harder (since it reads it as pausing auto -> movement, maybe?), which sucks since when using auto this results in me suddenly realizing my party's getting way more hurt than they should because a guard's up but then failing to break it when I rush to do so, but that's just anecdotal...
and then there's the bow glitches, though I don't really play bow so I can't speak to that