To my opinion Winston is not victorious, but who can in such a society!
Well, I think that Winston is both victorious and defeated but in differnet manners. Winston has been defeated by the party. They have managed to indoctrinate him with their senseless dogma to make him 'love' Big Brother and follow their word. He has lost all his individuality as you said, and no longer has a thought of his own and is basically a zombie with thoughts put into his head by the Party's propaganda.
But winston is also victorious without himself knowing it. When he shed a tear when he met Julia in the park after being in room 101 the tear represents the fact that even though they have managed to make him believe everything they say unconditionally, there is still a part of him that he doesn't realise is there. Although he thinks that he no longer has any feelings for Julia, that one part of him shows hope as it shows that he does still has feelings for her but they have been covered with layers and layers of the propaganda that he no longer is able to notice it;s presence. So in that way he is victorious as he has been able to keep one small part of his soul away from Obrien during the torture and keep a small part of his individuality, although he and no-one else is able to recognise it anymore. So basically it's like a unrecognisably rebellion.
This is shows that no matter how much propaganda, torture and fear totalitarian regimes like Big Brother uses, they will never be able to fully convert everyont,