To put it simply;

Dantes is Servant with two aspects, similar with Charlemagne.

Him as the betrayed fisherman (pre-Dumas writing, like Carl), and him as an avenger rich guy (post-Dumas writing, like Charlemagne).

The one summoned by Chaldea (AOE Avenger) is the fisherman ones. He decided to help Chaldea as he represent 'willpower', unlike his fictional ones (ST Avenger) who represents 'revenge'.

That's why 'they merged, then split again in OC 2'.

This 'split' decision is because Type Moon writers are big fans of Gankutsuou anime.

There was interest for Dantes as a SSR Avenger, but they unsure to fully commit to it (they're more than ready to make him OP Servant) so they play it safe with fisherman side of him. Turned out Dantes is popular enough, they put Monte Cristo on shelves.

So, Monte Cristo is post-Dumas writing Dantes and that one represents Revenge while Dantes is fisherman who, while still having his vengeance stuff and etc, is pre-Dumas writing and is kinda his past-self when he was beginning his vengeance, am I understanding correctly or did I misunderstand what you meant here?

Yes, their appearance tell enough, I believe.

One began with shirt, then gain coat. The other one is nobleman turn into a monster-like figure. Their interactions with Hans, Shakespeare and OG Rulers, follow this difference as well.

Dantes is excited to sit down and talk with the writers,

He view Jeanne and Amakusa as 'Wow, so Extra Class is not only Avenger'.

You could say he still got a young man positivity inside despite all the "KUHAHAHAHA!"

Monte Cristo OTOH is reluctant to talk with writers, ended up join them because he's Dantes.

His response to Jeanne and Amakusa is about to be drown in vengeance is normal as bonds are beyond anyone control.

Alright, just was making sure I didn't misunderstood.

So, Monte Cristo is Dantes that we have in our head, the one who was protecting us while physical one is fishermen, Dantes who was at the beginnings of his revenge and is still positive dude, but then they merged into one being to fight Alessandro that infected us with him or smth, then after they split, Willpower/Past Dantes has appearance of Dantes we know and love from before while Determination has, yk.

Did I understood everything correctly? Also thanks with explaining this, I REALLY appreaciate it