That has to be a local issue, because that is flat out wrong. The majority of all e-commerce sites does exactly that. I have yet to meet a PSP that believe send the entire credit card number, expiry and CVV was the right solution. I've talked to exactly one PSP that supported accepting credit cards in an iframe, and that was only available to existing customers, because they where discontinuing that service.

In most of northern Europe at least, customer have been use to credit card payments redirecting them to third party sites since at least 1999. It has zero effect on conversion.