There were NO legal impediments to data sharing when Hoover was in charge...and yet there was little or no data sharing.
You can have all the small, independent intel collectors you want, but if we don't have someone to put their little pieces together, we are back to square one.
Now, if you give the intel czar the power to hire and fire the directors of these small services, then I might agree with you. But that's the only way he's going to get their attention and make sure they share the intel they collect. Any other arrangement is, as they say, reshuffling the deck chairs on the Titanic.
I agree, he should have the power to hire and fire the heads of the different agencies, but how much power over the purse should he have? I think he should get a grant fund, but the other agencies should have their budgets handled as they are now.
The grant pool that the director has can be applied to any of the departments under his control, at his discretion. At the end of a budget cycle, he has to report and explain his spending, but that's only normal.
So the agencies are funded as they are now, and they get supplemental funding for special task/mission oriented projects from the director of intelligence. They can also apply to him/her for additional funding, or they can go through their normal methods for funding. It just depends on how fast they need the money. The director can disburse money faster than the legislator, etc.
Oh, there are different schemes...
But the Director of Intelligence should have the power to hire and fire the directors of the agencies under him/her. They'll still have to justify the decision later, and any hires could go through the current nomination and approval process in the senate. Etc, etc.
Ideas only... But I think an interesting starting point.