I would be careful about this assumption -- the old PP link is still there but others have reported it to be a zombie and on the United page if you go to the credit card page PP is not listed. So do you find the link by search or by following a link from the active pages?

Note there have been 2? reports of successfully get upgraded to PP card in the past 12 months, so not impossible but does not seem to be standard and many have been declined.

CPU for silvers are rare on hub-hub flights but may be better on some spoke routes.