So while this new entity has all of Data's memories, he still has Soong's brain structure, which could mean he'll retain aspects of Soong's psychology or personality. Or that the parts of the two beings could synergize in unpredictable ways.
And again, my point is NOT that anyone has to believe it really isn't Data or that it really is. My point is that it doesn't matter. Those who want to believe it's the same being are perfectly able to do so if that's what satisfies them. But those who want to believe it isn't are equally justified to come to that conclusion. There's no point arguing over it because it satisfies both groups.
But whether you think it's the same Data or not, he's still changed. It's not just a return to the status quo. He won't just be back at the ops station on the Enterprise giving exposition. He's got a new outlook on life, a new set of goals. He's turned down the offer to return to Starfleet and gone off on a new quest of his own, seeking the Commonwealth of AIs. He can even use contractions freely now. As I've been saying, if you're going to resurrect a character, that's the right way to do it -- by making it a new direction for the character rather than just a lazy reset.
Everything you've stated here points to Data 2.0. I'm not sure how anyone can interpret it any other way. Different body and different operating system plus not having all of the originals memories. How could he be the same person when he missed a defining moment of his existence?
Our resurrected Data is a copy of the original. A clone from a memory perspective. I'm not criticizing the method, I personally think it was the best we could hope for.