Is he really being a dick about it? Lionel Messi isn't Leroy Sane. He's the biggest Footballer around. I can't criticise the man for not wanting his biggest asset on and off the pitch to leave. He's doing what every owner would do if they had Messi.
It is coming across as desperate, but if you loved a woman and she said she wants to break off the marriage because of the way you've been with her for the last 3 years, you'd fight to keep her to make it right. That's all that Bartameu is doing, and he's well within his right to do so.
The best we can hope for is Messi not making a decision and dragging this out even longer- maybe another 2-3 weeks without this going to the courts. If he does that Bartameu may have to accept that Messi will not change his mind and negotiate a fee.