off the mark, beside the point
彼の言ったことは的はずれだった。
What he said was beside the point.
君の言うことはまったく的はずれだ。
What you're saying is completely beside the point.
今の質問は証人を責めるだけの―的はずれな質問です
That question was completely beside the point and served only to blame the witness.
— ア・フュー・グッドメン (1992)
あなたの推量は的はずれだ。
Your guess is way off the mark.