As mentioned there are legislative limits to how some of these organisations can act. CSE and CSIS are pretty-well mutually exclusive - one (CSE) is a SIGINT org prohibited from domestic int collection, and the other is a domestic security org with limited foreign collection capability. Where they can, they certainly cooperate, but it would be a mistake to put them together.
As I understand the role of PCO on the int side, it acts as a committee to fuse the int from various orgs into a "common picture" to present to decision makers in the PMO. The goal is to avoid conflicting reporting, which is/was an issue in the US, where the CIA, NSA, FBI and DIA may well have differing interpretations of the same source. Given that those US orgs all had/have independent access to the Executive, it could create confusion.
Teddy makes a good point: PCO doesn't have an "act" function. It is essentially an All Source Intelligence Centre writ large. I think I understand your point about an agency divorced from PCO.
While I think that there could be some rationalization of what currently exists in Canada, I don't see the creation of a mega-bureaucracy as the solution. It may speed up the reaction time, but at what cost? Neither do we need to start expanding the powers of existing departments 'till they overlap to the point of duplication.
Acorn