How about this for an agreeable solution:
1. The writers don't know the distinction between sentience and sapience
2. Data was not having a scientific discussion but reciting poetry, which is often filled with metaphors and other less concrete, fact-based notions than a scientific journal article
3. Data was employing hyperbole. Regardless of your position on feline consciousness/sentience, there is no question that compared to humans and Data, Spot's level of sentience is miniscule. Therefore, it would fit a hyperbolic poetic convention to imply that, compared to humans and Data, cats aren't quite up to par. He might have simply been exaggerating.
4. At the time the episode was written, the studies people referred to were either non existent or not widely known. Back then it's not unreasonable to think that even animal advocates didn't consider cats to be sentient. (And of course there was no Wikipedia or Google Scholar for them to consult, nor had the EU yet declared by law that animals are sentient.)
Now I'm a huge cat-lover. Unfortunately, because of terrible allergies and asthma, I can't be inside a house with one. But I've almost always adopted stray, unwanted cats and given them as much care as I can. They seem quite happy having the safety, shelter, and free food/treats/attention, even though I sadly cannot keep them inside with me. But the climate where I live is very mild. It rarely gets below freezing and hardly ever snows (and the summers are mild).
I have no idea what goes on in the minds of my cats. But they seem intelligent enough, and I would *never* want any pain or sufferring to happen to them. I know they have feelings and brains. As an electrical engineer who specializes in biomedical engineering and brain injuries and disorders, I'm quite attuned to the latest developments on the study of the human mind. One thing I know is that it's an extremely poorly understood organ. So I imagine it is difficult gauging with much precision the level of cognition of cats except through analogies to humans and behavioral studies.
I would hope that irrespective of the posters here who represent a wide spectrum of beliefs about cat sentience that *all* would agree that (a) we must treat them with the utmost kindness, ensuring that, as with our fellow humans and other animals, no preventable harm/sufferring visits them and (b) whatever their true sentience is, it's nothing *close* to that of humans.
Plus, the inability to communicate verbally with them makes it that much harder to discern their actual thoughts!
Now can't we all get along?

(seriously though: I'm not actually suggesting you guys don't have the right to continue to go at it! I'm just trying to offer what I think is a decent resolution.)