To say that "curates were as well educated as the rest of them" is to damn with faint praise indeed. To quote Halevy's England in 1815:

The descriptions of Gibbon, Bentham and Jeffrey have rendered the intellectual torpor of Oxford a byword. . . . Nor did the University impose upon candidates for the degree of Bachelor of Arts any examination worhty of the name. Three questions made public in advance in theology, logic and grammar, the answers to which existed in a stereotyped form and passed from candidate to candidate, followed by a dinner with the Regent Master who had examined the candidate, constituted the entire examination. . . . In 1800 a system of genuine examinations was instituted.

[18th century Cambridge, in Halevy's view, was both somewhat more intellectually active and more zealous in religion.]

Both universities were suffering from a radical evil that was due to the composition of their student body. No doubt at Cambridge, and even at Oxford, there had been for many years past an elite who worked hard, who even at times overworked themselves to prepare for an examination. But the grat mass of undergraduates were deliberately idle.

In sum, a man could get his degree at Oxbridge in the 18th century along with an education or not, pretty much as he chose. In the absence of the modern sytem of tenured academic places, I suspect that a good many Oxbridge graduates who did have intellectual inclinations took orders because the Church could provide a secure income, a respectable position, and the leisure to pursue their intellectual interests. Where else could they go?