Your belief about Barr is fundamentally incompatible with Barr's belief about Barr. The real Attorney General, in words and in deeds, favors a unitary executive who, by dint of national security argument, has almost unlimited power including the ability to spy on anyone they please.
While you may believe he is taking on the FISA court, and there are abuses there to fix, by Barr's own admission he doesn't seem to think there are any restraints on an Executive's power in the realms of national security or foreign policy. It seems to me the motivation around FISA is strongly motivated not by sincere belief in the limitations of executive authority, but because of a sense that they (read: the President) were wronged.
When Attorney General William Barr spoke to the Federalist Society in a memorial lecture just a few months ago[1] he lamented the transparency Congress has forced upon the Executive, "There is no FOIA for Congress or the Courts. Yet Congress has happily created a regime that allows the public to seek whatever documents it wants from the Executive Branch at the same time that individual congressional committees spend their days trying to publicize the Executive’s internal decisional process. That process cannot function properly if it is public, nor is it productive to have our government devoting enormous resources to squabbling about what becomes public and when, rather than doing the work of the people."
Barr then attacked the judicial branch directly, claiming they are "encroaching on Executive responsibilities in a way that has substantially undercut the functioning of the Presidency" and in particular, those darned judges keep finding that they can review the acts of the Executive! Isn't that frustrating?
He writes in such an example: "Courts are now willing, under the banner of judicial review, to substitute their judgment for the President’s on matters that only a few decades ago would have been unimaginable – such as matters involving national security or foreign affairs.
"The Travel Ban case is a good example. There the President made a decision under an explicit legislative grant of authority, as well has his Constitutional national security role, to temporarily suspend entry to aliens coming from a half dozen countries pending adoption of more effective vetting processes."
Do you think that a surveillance state reformed by Barr would really rein in the courts, or simply remove them from the picture?
[1] - https://www.justice.gov/opa/speech/attorney-general-william-...