Does this make any sense? Somehow Microsoft did exactly what Sony was already doing with Rocket League since launch and turned it into a knock against Sony.
What are you talking about? Nobody's "knocking" anybody by saying "the ball's in their court". Sony has supported cross-platform play with the PC, yes. Microsoft has supported cross-platform play with the PC, yes. Now Microsoft is open to cross-platform play with the PS4. If Sony is as well, they should be able to figure it out.
Of course there are rules, every part of the development process has rules. You don't just say "here's our network, go nuts" unless you don't like having a network much. The goal should be to accomplish true cross-platform play, not making sure the other team doesn't get a "point" against your team.