Sansa saying “Winterfell is yours” is just welcoming her to Winterfell not giving it up to Dany. Ned send the same thing when Robert came in the first episode. It doesn’t literally mean Winterfell is dany’s
I really have no desire to sit here and quibble over semantics, but oh well here goes. Monarchy defined:
Monarchy (n.) - A monarchy is a form of government in which a group, generally a group of people representing a dynasty (aristocracy), embodies the country’s national identity and its head, the monarch, exercises the role of supreme sovereignty.
When there is a monarchy, every territory that is part of their kingdom is under their control and subject to their will, period. That is how monarchies and oligarchies have always worked. A queen is, by definition, inherently a monarch. So even if “Winterfell is yours” as spoken by Sansa in the moment is symbolic welcome instead of literal like you are claiming, symbolic relinquishment of control is still relinquishment of control. In the grand scheme of things, there will be no functional distinction. Or else what would even be the point? Why even make the North kneel? Saying “the Starks dont’ control the North but it’s still their’s” doesn’t really make sense. How is it theirs if their ownership of it is still subject to the power of another? That’s more like renting, not buying; they have a lease, not a mortgage.
Also, that is simply not what was said between Robbert and Ned? Especially when you look at the context of their conversation. This is literally their dialogue:
Robert Baratheon: Nine years! Why have I not seen you? Where the hell have you been?
Ned Stark: Guarding the North for you, Your Grace. Winterfell is yours. (1.01)
They don’t say this to every visitor who shows up at Winterfell, it’s not a standard greeting. I’m pretty sure it doesn’t play on their answering machine and isn’t printed on their Christmas card. There is nothing to imply Ned means “the North is yours… but not really lol.” I’m not entirely sure where you are getting that interpretation from or what you are basing it on, but I don’t see any evidence for it. Not in the actual words spoken or any other subtext. Again, that is the entire function of monarchies and how they have always operated. If it wasn’t why have them? Like, I’m sorry, but that’s just a really strange, and honestly pretty patronizing, retcon of the practice of monarchical power and I don’t quite know where you’re getting it from.