I understand where you are coming from, and think you make a valid argument. I did poorly word my response, but stand by my statement that inviting non-Catholics is a good thing.
Regarding a joined/unified liturgical event, I think you are right. Pius XI clearly teaches that shouldn’t take place.
Regarding pre-VII, my opinion is that the Church had a much stronger position in the world, both as a moral authority and political power, thus negating the need to have events like the Pentecost meeting.
Inviting is one thing, praying with them and giving legitimacy to their religion is another. And when there has been no clear indications that he believes there is an absolute requirement for any non-Catholic to convert to Catholicism his invitations appear as empty gestures. He’s (and we are) better off not inviting in the first place.