DL and WS actually withdrew their application for a joint venture when the US Government told them they would have to give up slots at LGA to get it approved.
I’m a bit surprised that there is not some JV standard for premium economy service that the carriers have to meet. VS and WS are outliers serving drinks in glass cups — DL did when they introduced Premium Select but then switched to plastic due to a galley configuration issue I think.
The market for international premium economy is strange… pre-COVID it seemed to be replacing J in company travel policies, though it seems to have picked up some high-value leisure travelers. Airlines seem confused as to whether it’s a part of the economy cabin, e.g. LH recently eliminated complimentary spirits in both Economy and Premium Economy.
UA also serves drinks in actual glass in their PE cabin (though I believe only during the meal service times). Same with AC. I do not believe AA does, however.
As for WestJet, we should remember that their PE is their domestic F cabin. They only sell J if there is a lie flat seat