I notice there's a number of abilities that apply some condition such as Immobilized, but then have a Fitness check to resist or remove the effect. These don't tend to scale into higher level play, so these abilities become pretty useless.

I'm not sure if this is intended (high level targets are basically immune to effects, and so are the players).

There's a lot of TN3 Fitness checks to resist conditions. At low level (Skill 2, Ring 2), these are very effective (28% chance to resist). At high level (Skill 4, Ring 4), these are pretty useless (93% chance to resist). A couple of these abilities let you spend opportunity to increase the TN to resist, and that's a decent solution, but most of them don't have that option. Often, even when they do have the option, it's competing with other opportunity spends, so it becomes unlikely to be applicable. Some abilities, like Channel the Fire Dragon, might be better served by having the bonus successes increase the TN instead, though this only works for abilities that aren't already applying those bonus successes to another effect, like fatigue.

Spoilers:

In the sample adventure, there's an adversary who gets Immobilized by the Jade Labyrinth ritual. Even with a low skill of 2, the adversary has enough rings to escape this 90% of the time before it ever restricts movement.

They scale with Wounded and Gravely Wounded.

And with health-based adversities, too, in many cases.

Also, I recall some of those abilities might have specific opportunities expenditures to increase the TN to resist. Not all, but that’s easy to add if it becomes a problem. With higher dice pools to start with, it’s more likely to get more opportunities.

Still it might be the case that some abilities are not supposed to scale: a rank 1 kata might work well on rank-and-file mobs but it is not shocking that experienced adversaries can easily resist them... as long as there are higher level kata out there who also bestow effects and are harder to resist (but also harder to pull off).