Yes, buyers who pay with a PayPal account would use the email registered to their account, which should be a valid email, but buyers without a PayPal account who use the option to pay with a card on the PayPal checkout site could conceivably enter a bad email. Unfortunately, we have no control over that, as that's handled entirely at PayPal's end.
You might consider adding one of the other payment services we support to handle direct card payments through our own card-checkout screen, which does require entering the email twice. Then you could disable the card-payment option for PayPal checkouts by setting PayPal Account Optional: OFF in your PayPal account under Account Settings (️ gear icon) > Website Payments > Website Preferences.