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.
You're delusional if you still believe this.
Edit: and yes, there is plenty of evidence that especially during the Vietnam war the CIA was actually breaking the law.
There is no paper trail for this abuse. This is a system that should not exist.
But I know for a fact that the CIA does have a committee of elected officials that oversee it. Whether that is effective oversight is debatable, but the fact is that it exists, and they must legally disclose their actions. This means there are legal means by which they can be held to account in the cases where they do not.
And they let their own inflated egos delude themselves in believing that the overall threat posed by the Russians/Chinese (which in comparison to the US, are much weaker) is greater than that of a government that surveys/records/interferes with the lives of its own citizens.