The problem with most single-system analyses

Saw this tweeted by a trusted source Sunday morning, but HuffPo published an op-ed by Green Party of Ontario leader Mike Schreiner on March 15 regarding merging Ontario's four publicly funded school boards into two.
As readers here would know, I support this, with the full disclosure I am the product of a Catholic school system. However since becoming a ratepayer in southwestern Ontario, I am an English public school system supporter (for whatever that's worth in a single-funder system).
Schreiner's POV in this latest piece hasn't changed since the last Ontario election. He's consistently been a single-school system supporter since taking the mantle of the GPO. The challenge, however, is that Schreiner leads with the financial argument. That argument in this case is based on a 2012 study by the Federation of Urban Neighbourhoods of Ontario Inc.
There are some assumptions in that report upon which the estimated $1.2 billion to $1.6 billion (my rounding) in annual savings are based that are false. They appear to be based on a presumption that many of the students currently in Catholic schools would leave the publicly funded system.
That's the only guess I have as to how the study identifies efficiencies of scale to the extent it does. It pegs $164.9 million in savings from the elimination of school board and governance grants if the province's Catholic district school boards were eliminated. This assumes the public systems taking over management and governance of the physical assets and students would be willing to have that added to their existing workloads.
I don't see that happening.
So you wouldn't see 100% of those governance and admin costs evaporate.
It pegs $169 million in student transportation cost savings-- by increasing walking distances across the province and the elimination of duplication. Again, I don't see the savings fully realized as school board transportation consortium shotgun weddings started taking place over five years ago and are pretty much fully implemented.
Which isn't to say some of the estimates presented aren't valid-- savings will happen in capital and facilities as we use the existing stock of school buildings more efficiently instead of having wide discrepancies between public and Catholic schools that lie within blocks of each other.
Where the financial argument falls apart is the economies of scale line, where it estimates $487.9K to $813.2K in annual savings.
If the number of students in the system remains stable after the merger of Catholic and public boards, the overall costs of running the system are not going to dramatically drop. Yes, there will be savings in some areas where there is duplication-- but overall you're not going to suddenly have 40% fewer principals or superintendents. The number of teachers and support staff would remain relatively static.
It surprises me neither party in this example has bothered to look at Quebec or Newfoundland and Labrador, where systems were merged. What sort of savings have materialized? You might find some concrete examples there instead of assumptions built on false premises.
It's an argument that side-steps the conversation that should be happening around publicly funded faith-based education in Ontario. Which is whether it should be publicly funded at all. Arguing it shouldn't be funded because of potential, flawed estimated savings is a weak foundation because those "savings" simply won't materialize to the stated degree should Ontario move to a single system.
Ontario is no longer part of a dominion where a minority of Christians need to have their faith protected from being extinguished by the majority of Christians. Those days have long passed-- defense of any faith should be a matter of instruction and practice within individual families and whatever congregation they choose to associate with, not a publicly funded educational system.
That -- and not money -- should be the No. 1 reason for a single system in Ontario. I've not yet heard a politician frame it in those terms, which is unfortunate because the other arguments only distract from what should be discussed.