Well, I see it differently. I'm not convinced it is a great trade. I am assuming that they are confident that he will sign longterm with them because that's a lot to give away for one year. Yes, the NYY can buy whatever they want and Yes, Soto has great stats but he certainly was not a difference maker in SD.
I believe that Cashman is panicked and is trying to save his job. All those things can be true. The yankees have been an average team (most years) for a long time now. No team can trade multiple assets for single assets consistently and not get old and unatheltic like they have been for the last few years.