It’s wild fun now debating, but prove incompetent (2,5,7)

I believe the answer is:

be found wanting

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'prove incompetent' is the definition.
I can't tell whether this definition defines the answer.

'it's wild fun now debating' is the wordplay.
'it's wild' indicates anagramming the letters.
'fun'+'now'+'debating'='funnowdebating'
'funnowdebating' anagrammed gives 'BE FOUND WANTING'.

'but' is the link.

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I've seen this clue in The Times.

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