Those are my thoughts, if DL and its partners are providing me with a pleasant travel experience and tends to my needs sufficiently, I may as well enjoy the benefits of that status, whatever they may be.
But nothing wrong with diversification if it provides beneficial status with another alliance.

And lest we forget (but not multi quoting from several posts) that most HVFers aren't FTers, and will just take their preferred airline and routing, whatever it may be, at the price they're willing to pay, and the FF program is secondary, or they're flying on a corp contract. I doubt that a material number of HVFers are jumping ship to the competition once meeting the tier threshold. But after a year or two, DL will be able to have some good data on this.