To be fair to the USN, they are looking at drone ships, which clearly have the potential to be a 21st Century Frigate in some respect. But if you look at traditional roles of a navy, any navy, they include maritime blockades, stopping and searching, search and rescue, even combat against lower end surface threats. Some of those can be undertaken by a drone ship, but not all, and yes, use drones as pickets and supplements to maritime forces. But dont pretend, as some do, that its a substitute for manned ships. That only seems to work for the Israeli's, and they still have a fleet of manned corvettes.
I think the problem with the USN that I can detect, it lacks pragmatists. It lacks people who reject the very best that money can buy, and are willing to buy lower end platforms, that they specify room and development space on to bolt on new weapons or systems, that they throw the money at like no tomorrow. I dont know if that implies a 21st Century OHP, or something like type 31. But it implies people rejecting silly ideas like the Seawolf, or the Zumwalt or the LCS that anyone with some common sense would see were not affordable in the post cold war world. Alright, new cold war world. Nobody is still stumping up for it, and if they did, its still leaving seaspace uncovered.
Bring back the Flower class!