More human than human isn't just an advertising slogan. It goes to the heart of both films.
As for the question of whether Joi is sentient. You can look at in a purely commercial sense a simple machine that has basic responses would not sell very well for very long. One that is smarter and able to adapt and behaves indistinguishably from a normal human or replicant would sell very well. One that is able to adapt really well to its human companion would actually have to be smarter than the human.
Whether its sentient or not who knows. The people in BladerRunner dont believe the Replicants are sentient or have souls either.
In both films there's an inkling of an eco-feminist critique. I can dream that some day there will be a film linking the fragmentation of humanity (portrayed in both films by the free licence to kill those who aren't human enough) directly with what is happening to the planet.
I know the off-world colonies are supposed to be wonderful, and it might be very dangerous to expose them to the kind of ecological critique we see in both films. But seriously, does any modern human imagine that the societies of the new colonies are any less shitty than the mess on earth? It will be the same story there: a tiny stratum of elite rich lording it over indentured servants, freedmen and slaves.