These lines are in the verses 'On Paradise Lost' which appeared originally in the 1674 edition of that poem. Johnson might well have gone further and made the poem prophetic of the real result by quoting—
' Pardon me, mighty Poet, nor despise
My causeless yet not impious surmise.
But I am now convinced, and none will dare
Within thy labours to pretend a share.
Thou hast not missed one thought that could be fit
And all that was improper dost omit:
So that no room is here for writers left
But to detect their ignorance or theft.'