It would definitely be unusual in the various American Englishes that I’m familiar with. “Have seen” is present perfect, and it implies something ongoing (“I have seen The Birdcage over 100 times so far”). “Saw” is the simple past tense, as in “I saw The Birdcage again yesterday.”

It just strikes me very similarly to when a non-proficient English speaker misuses a contraction like “I would like to know what time it’s.”
And honestly, I think language science should be more descriptive than prescriptive in general, and I recognize and respect regional variations. “I seen her yesterday” is a dialect variant you’ll hear in some US regions.
It would definitely be unusual in the various American Englishes that I’m familiar with. “Have seen” is present perfect, and it implies something ongoing (“I have seen The Birdcage over 100 times so far”). “Saw” is the simple past tense, as in “I saw The Birdcage again yesterday.”  It just strikes me very similarly to when a non-proficient English speaker misuses a contraction like “I would like to know what time it’s.”
And honestly, I think language science should be more descriptive than prescriptive in general, and I recognize and respect regional variations. “I seen her yesterday” is a dialect variant you’ll hear in some US regions.
It was really more about the irony.