I would imagine that using an LLM model for secondhand thinking would be seen as a bit decadent and reflects a weak will, easily influenced by the illusion of authority.

The Will to Power, as far as I understand it, is about how resistance (or friction) produces the strength of will to overcome obstacles. AI does the virtual opposite of that while also commoditizing cognition.

I'd agree with the other commenter that Nietzsche would probably see this as just another reversion to Plato's Forms - LLMs, by nature, are median outputs of cognition. There is no ubermensch to be found amongst the lowest-common-denominator, only the narcotic allure of becoming increasingly, as the kids say, smooth-brained.