I really think Bartomeu wants Messi to take the to court so he can try and portray him as the bad guy.
I'm pretty sure it's just an opening negotiating position. Don't watch what they say, watch what they do. I see two underlying themes
'It's the economy, stupid' - Their financial position is supposedly poor due to their wage bill. Bartomeu would be liable for losses come March. He knows due to the state of play he won't be re-elected in March. A rational position would be to extract the maximum transfer fee he can and get the highest wage earner off the books. I wouldn't expect to see a player swap because that does nothing for the cash situation. Likewise I struggle to see the sense in keeping a very unhappy and demotivated player, unless there are commercial considerations.
'Actions speak louder than words' - if they wanted to build the future around Messi then I don't think we'd see them dumping his best mate over a phone call, telling him 'your privileges are over' and refusing to meet with him. This isn't how you reconcile and persuade, quite the opposite.