As you accept elsewhere, there is the law, and there is reality. Oversight is captured; the intelligence agencies and surrounding industry has been given almost everything they wanted, even retroactively[1].
Information sharing has also removed a lot of practical barriers; what does it mean for the CIA to be constrained if they can use other agencies for domestic work? Interdepartmental rivalry is still a constraint, but hardly one to count on.
When thinking about the value-add of agencies like this, analyzing black-letter law is close to useless. You have to look at what actually happens. Tricky, that, when talking about spies.
[1] One interesting question is how, as a practical matter, to provide systematic oversight of spies with the ability to monitor and anonymously leak details of the overseer's lives, blackmail/manipulate third parties, and selectively leak to the media.