Yes, preview is generated by the sender to avoid receiver's address leak to a sender-controlled host, but what I'm saying is that WA should enforce on the receiver side that both point to the same URL. As said initially, they are most certainly doing it this way to unfurl URL shorteners, which would other be the easiest way to phish people. At the same time it's also noteworthy that the preview can fail to be generated on the sender side and the message will be send out anyway, so yeah, I agree with you that they could just remove the preview feature. Probably in their opinion the trade-offs are worth, I guess.