But if someone decides to start shooting back, we'll need something with actual sensors and weapons to escort these "frigates."
I think your expectation for the navy is too high.
I give you two routes - either the navy starts building something while adding and changing the design as it gets built, or it starts building a flight while it designs the next one, and introduces capability by each flight.
Option one led to disaster already. After reading through 49 pages of this thread, it's still not clear to my why FFG(X) got cancelled. If the design was already finish and the navy was happy with it, it makes no sense to build two ships and stop. Clearly - there had to be multiple reasons beyond simply "politics" that results in the cancellation - either the cost is too high, or upgrading it is a pain in the ass, or the modifications made have resulted in either of the first two reasons or, and god damn it to hell, the navy wasn't done modifying it yet.
With option two, you still are building as you design, but at the very least you are putting hulls in the water, systems to the test, and experience being accumulated. In the meantime, your cost and production isn't constantly being kneecapped by having to put in stuff and rip it back out again to accommodate new upgrades.
You have to learn to walk again before you can run. China didn't build 055's on day one either did they? We might not be on day 1 here, but we certainly have regressed backwards enough to learn to walk again - and the earlier we all face that reality the faster we move on from it. I don't have high expectations for FFG(X) in the near term, but I'd rather they screw this one up than DDG(X). It could be that this NSC based design is an interim solution too.