A redundant “of“ in all kinds of locutions popular among the baseball crowd some forty (or more) years ago surfaced on TV broadcasts and started the plague:
....it won’t be that long of a speech, that difficult of a shot, that big of a mess, not too good of a looser, how good of a shape is she…. You can make them up as you go.
Then it got (muchly) improved: Adjective? Who needs it. An all-purpose “much” will do: that much of a speech, that much of a shot, that much of a mess, how much of a shape, not too much of a looser…
Reader’s Digest (1983) and Copperud (1980) condemned all of them as nonstandard and erroneous. Even Webster’s liberated (call it “woke” today) Dictionary of English Usage (1994) felt obliged to say something about the disease:
“The only sure thing is that when normative usage writers encounter these idioms their reaction is to condemn.”
Nevertheless, the paragraph that followed was “back to normal” for Webster’s crowd:
“But the only stricture on it suggested by our evidence is that it is spoken idiom: you will not want to use it much in writing except of the personal kind.”
Too bad your Longmans and Macmillans didn’t have anything to say about that usage. Throw them away.