I mean I agree mostly with what you are saying, simply we have yet to see anything or have any statement about them not buying that IP.
Unless stated, I believe its correct to assume its owned by Sony as I'd argue that would be something they would state today if anything if they are willing to tell us all this. Like with future Destiny titles, future new IP, stating they are self publishing.....yet not say they own the IP? Sounds like its not stated cause Sony bought it, which would make sense for 3 Billion and allowing them to have creative freedom, self publish for selling that IP in the first place. So I don't see enough to say they didn't buy that IP, Sony doesn't buy teams like that and I don't think any major publisher to my memory have ever had a deal this big, with the IP not being owned by them or something.
Even more odd, Sony owns Bungie, they bought them, thus the IP is owned by them by default anyway as this isn't some long term marketing deal we are talking about or some timed game, its simply too much money spent to believe they don't own that IP. Would be the first I've ever heard of such a thing at this price point in the industry.