Hajduković to Milatović: Open Balkans is goodbye Europe now

Montenegrin scientist Dragan Hajduković sent an open letter to the newly elected President of Montenegro, Jakov Milatović, in which he tells him, among other things, that it is impossible to advocate for the European Union and the Open Balkans.
We remind you that Milatović stated that Montenegro should be part of the Open Balkans, stating that "it is better to be part of the Open than the closed Balkans".
Hajduković told Milatović that the EU and the Open Balkans initiative are mutually exclusive.
We are transcribing Hajduković's letter in its entirety:
Mr. Milatović,
First of all, I wish you to be a successful, very successful president of Montenegro. My desire has nothing to do with you; I would like to wish success to everyone in your position, because Montenegro needs the quality work of the president. I am sorry in advance that my wish for you to be much more successful than your predecessors will not come true.
I am writing to you because of your views on the European Union and the Open Balkans.
First, both you personally and your Europe now movement want very fast entry into the European Union.
Second, you personally want Montenegro to join the Open Balkans.
I fully respect your right to advocate either for the Open Balkans or for the European Union, but it is impossible to advocate for both, because they are two incompatible projects that are mutually exclusive. It can do one, it can do the other, but it can't do both.
The open Balkans is exclusively for countries that are not EU members and practically means giving up the individual entry of these countries into the EU, while leaving the hope that one day they will join the EU collectively. So, the Open Balkans means giving up early membership in the EU; The open Balkans is goodbye Europe now.
Let's imagine that tomorrow Montenegro becomes a member of the EU and part of the Schengen zone. In that case, Montenegro's membership in the Open Balkans becomes impossible, because our neighbors could only come to us in the same way as they go to other countries of the European Union. For the sake of clarity, I ask you to answer publicly, and I ask the citizens to each answer for themselves the question whether the Balkan countries that are members of the European Union (such as Bulgaria, Greece and Croatia) can enter the Open Balkans (if they want to).
I repeat, the Open Balkans and the European Union are mutually exclusive. You either don't know that, or you do, but you're deceiving us. In both cases (ignorance or deception), my wish, that for the good of Montenegro, you become a better president than your predecessors, will not come true.
Otherwise, my principled opinion is that the biggest decisions, such as the EU or the Open Balkans (and earlier NATO) should be made in a referendum, and not by the will of individuals.
With respect,
Dragan S Hajduković