I'm...pretty damn sure that's not how her power works, or what kind of state she's in psychologically. She suffers serious psychological effects from near-constant power use from a young age, but she absolutely doesn't lack sapience whenever her power is not encountering a blind spot. It's just fundamentally nonsensical. Otherwise she'd act like a small child whenever near a power nullifier (like Mantellum), which she didn't in canon. Otherwise she'd be like a small child whenever dealing with a blind spot (she isn't). Otherwise she'd never be able to do anything with her power, since she couldn't actually decide upon/modify/prioritize/refine her Paths.
Yes, using her power like she does has a major psychological toll on her, but that's because she constantly uses it, which she does because she's trying to do the impossible, with everything at stake. It's not because her power itself is overriding her sapience. She is fully aware of the steps in her Paths and actively decides when to change/modify her Paths, stop following one (or all) of them entirely, and what she's doing in real-time while following a Path. Her interludes makes this explicit.
Also, Entities do design their powers for the good of their users to an extent. Scion's interlude makes this explicit. Powers are designed in such a way as to not be detrimental to the experimentation of said powers--so a power that drives its user insane (to the point of not getting as much useful data) is undesirable to them unless that is exactly the point of that power. Similarly, powers are designed with limits (like the Manton Effect) to prevent them from damaging the experiment (like making a power so lethal that the user can just kill tons of people with ease, and no useful data is gotten, or a power that harms its user and gets him killed prematurely). Lastly, shards are (by their very nature) designed to be directed by the will of their users, not the other way around. After all, gleaning data from how the hosts utilize their powers is the entire point of handing out powers in the first place, and it is also how the Entities use their shards themselves (as in, how they use the ones they never intend to give out). While the Entities do program in some limitations and general protocol, they don't like the shards exercising much control over their hosts unless that is the specific purpose of a specific shard.