You can call that slavery if you wish. Remember that toward the end of the series they're reconsidering the doctor's status and all but admit that he's sentient/sapient.
I remember in Author, Author where they legally reaffirmed that he was not a person, even if his literature was seen to be his property. The holorights subplot was interesting, but it wasn't completely clear what it was a metaphor for, either something old like race, or something newer like orientation, or if the writers were just pissing in the wind with no idea that any one would ever look for depth in their work that they hadn't bothered to consider. I really thought sometimes that the holorights stuff was just a call out to nerds who were picked on by jocks rather than a minority who was more clearly defined.
Plus in endgame he seems to have all the rights of a citizen, given that he can even marry.
The Doctor might have been a special case, he might have had abridged rights, he might have still have had no rights (not a legal marriage), or maybe there was a very bloody civil war where billions of fleshies and billions of ligthbulbs all died over the lightbulbs desires to not to be forced to wait tables for the fleshies under a constant threat of death.
Okay, you might be %99 right about this, but you can't be %100 because there is no definitive answer, just endless grey and wiggle.
Consider this.
The Federation can make truly sapient holograms if they want to, but they don't want to, because that would be wrong. They intentionally make dumb unsapient/insentient holograms so that they are all still good people... But smarter holograms make for better servants, so they try to make them as nearly sapient (userfriendly) as possible without actually being legally sapient, designated by some legally approved/mandated threshhold of sapience.
A 24th century Turing test will be a lot harder to pass than a 9th century Turing test. Seriously in the 9th century, the Doctor could convince the smartest person on the planet that he was God, but 1500 years later he's at a loss to devise an argument why he shouldn't accept slavery as his lot.
This is the abortion argument.
Before 24 weeks it's a thing you can legally kill, but after 24 weeks it's a person and you will go to jail if you even damage the foetus.
(Oh boy!)
If the Federation is evil, and they only do evil things, then sure, Holograms are sentient slaves and no one cares, but if the Federation is good and only does good things, and holograms are sentient, then the Federation would free all the sentient holograms from slavery instantly.