United is getting rid of Global First. And as noted Polaris is years away from being common at UA. DL has the only all aisle access business class of any US airline and is one of a very few international airlines. Most airlines don't offer F, because no one wants to buy it. It's a free/upgrade cabin when it was offered.
As for the Residence, that's not even really F. It's closer to F+ since those flights also have The Apartments which are F.
Bottom line DL cabins might need a refresh, but they're the only game in town with a J product like what they have. Fly J on a lot of airlines and you don't even have 180 lie-flats.