When we compare this with his [Milton's] later prose writings, when he moved closer to the victorious Cromwellian ascendancy, we find that pragmatism usurped idealism, not completely but sufficient to suggest that for Milton the Civil War was a horribly educative process.
The above is from A Milton Sourcebook, by Bradford. The bold emphasis is mine.
It seems to me that 'sufficient' should modify a noun phrase, eg 'the almost complete usurpation of idealism by pragmatism is sufficient to suggest...'
Yet the original construction quoted above seems to need an adverb - 'usurped it sufficiently to suggest'.
In your opinion, is 'sufficient' an acceptable synonym for 'enough'?
Is the construction grammatically correct?
Is the metaphoric packaging (usurpation suggesting; war = process) confusing the structure?
Is the use of 'sufficient' here specialist in some way?