There is still room for city employees and other vendors to exert some control over higher level IT services and applications. But the core infrastructure needs to be under the control of a single competent vendor.
And the incentives are to keep it that way. As long as MS's PS team can make more money from one whale of a customer than they can supporting local districts, expect that this will remain.
Such that I don't think it is excusable to say "if only they had paid the professional services."
I am concerned with "best practices" in our industry, though. Too many of them are not geared to wide adherence and have fantastically bad failure cases.
Would you apply the same logic to road infrastructure? Why hire those licensed engineers...