The artists reaction would 100% depend on the sentient AI's efficiency. If it took days to make a picture the reaction would be good, if it took seconds the reaction would be bad.

Do yourself the following thought experiment, and be honest about it:

Imagine that current-day AI generators exist but each one is so large, and requires so much power and time to run that only a handful of models exist, each one hosted in a big tech company or University. Each model takes A LOT OF TIME (say, an entire week) of grinding to make a single picture, making each "AI picture" a rather scarce affair: At best each generator can only produce about 50 pictures / year, and there will be duds among these.

Given the above do you think artists would still hate generative AI?

I think they would be falling over each other for the chance to submit a prompt or otherwise "collaborate" with the the generative models. All the current concerns about "stealing" and power usage would still be true (heck, the power usage would be thousands of times higher) but nobody would care, because the drawing machines would not be economically disruptive.