There is crossplay between all 3 platforms! You can party up using the room code system :)
Yeah, absolutely! I definitely understand your frustration. I don't have access to replays (I wish I had time to build a system like that though!), so I'll take your word for how it went. I hope the MMR balances out for you, and your matches are close and fun :)
It's also important to note that MMR only adjusts when you complete a match. We've had issues in the past with people quitting out of losing matches and their MMR would only stay the same or go up on wins, creating a horrible feedback loop of harder and harder matches that they would leave. It doesn't look like you did that at all, so you should be good though!