Following the mechanics of an illegitimate council, accounts of Ephesus 449 reads like a blow by blow description of a riot, and is incredibly difficult to follow. The OrthodoxWiki simplifies it :
"The Robber Council of Ephesus was convoked by Emperor Theodosius II on August 8, 449 for the purpose of adjudicating the findings of the council of November 448 chaired by Flavian of Constantinople that had deposed and excommunicated the Archimandrite Eutyches for refusing to admit the two natures of Christ."
"The council was dominated by Theodosius, Dioscorus, and monophysitic supporters."
Histoians Brian Tierney and Sidney Painter, in their book Western Europe in the Middle Ages, 300-1475 state on page 38 that: ". . . it was thinly attended and packed with Alexandrians", in other words, a Kangaroo Court. Suffice it to say that credentialed delegates that could have attended either didn't attend or were ran away. Ephesus 449's only redeeming feature was that it was convened by an Emperor. It was deemed sufficiently authoritative as to require its overruling by Charcedon 451.
Let's compare to Dordt. Attendance was limited to Germans, Dutch, Swiss, and English, making it at best a Local Council. The French boycotted it, already clouding its legitimacy. No Papal Legate attended; Ephesus II at least had the decency to run off some of their Papal Legates. No Greeks or Italians were invited. The credentialing of the delegates was a farce, as the Remonstrants arrived fully exepecting to be delegates, but were instead arrested upon arrival:
The Arminians did not arrive at Dort until early December 1618. When they did arrive, their appearance turned into a farce. They were treated from the outset as the accused; a position which they rejected. (on pages 16 & 17).
. . . another Kangaroo Court. Let us also not forget the dirty power-mad machinatons of Prince Maurice, who engineered this Robber Synod:
The designs which Prince Maurice had long cherished against the ancient liberties and internal jurisdiction of the states, (each of which possessed by the act of union the complete management of its own affairs,) were then in a course of execution. By the forcible and illegal removal of the old burgomasters and governors, and the appointment of new ones; by the preponderance which these newly elected individuals gave to their own party in their election of persons to fill the higher offices of state in the various towns which had been ill-affected toward Calvinism and arbitrary power; and by the untrue and scandalous reports which were invented and industriously propagated respecting the alleged secret intentions of Barnevelt and the Arminians to deliver up their country to the Spaniards; the prince was enabled to succeed in his ambitious enterprises.
My position is that Local Synods may govern, but they may not overrule a General Church Council like Nicea, which actually did settle matters of Faith. Of the Church Councils surveyed, the least legitimate was Dordt, even less Legitimate that the Robber Synod of Ephesus, 449. Dordt was boycotted and ill-credentialed. Both Synods were packed for Kangaroo Court-style action. Ephesus II at least had some general representation and some Papal Legates. Of course, Ephesus II also had to be repealed with Chalcedon 451. Clearly, Dordt 1618 is even less binding than a Robber Synod.