Here are the parts where you gave good keypoints on how GOARCH decisionmaking bodies function:
Theoretically, it sounds like if the GOARCH leadership made a big enough "unorthodox" mistake, either in ecclesiology, doctrine, or administration, then:
1. Metropolitan Clergy-Laity Assemblies could elect "orthodox" delegates to Metropolis Councils.
2. Metropolitan Assemblies could submit amendments to Archdiocesan Regulations to the Archdiocesan Congresses.
3. GOARCH's clergy and laity could elect "orthodox" delegates to an Archdiocesan Clergy-Laity Congress, and the Congress could then adopt the Metropolises' "orthodox" amendments.
4. Do the Archdiocesan Congresses also elect any members of the Archdiocesan Councils? I am guessing from that the answer is Yes, because the 2018 Archdiocesan Congress voted on:
SOURCE:
https://clergylaity.s3.amazonaws.co...f-motions-from-2018-clergy-laity-congress.pdf
So it seems that in this scenario, "orthodox" Archdiocesan Congress delegates could elect "orthodox" delegates onto the Archdiocesan Council and could vote to give the Council with its new, "orthodox" majority sufficient authority that might be able to return GOARCH onto an "orthodox" path even if the Eparchial Synod desired otherwise.
But on the other hand, you wrote that "synods are the highest bodies", referring in particular to Constantinople's Patriarchal synod and GOARCH's Eparchial synod. Plus, Constantinople controls elections of hierarchs, so theoretically it could make sure that the Eparchy's synod of hierarchs agrees with Constantinople's stances on every issue, whether right or wrong, so long as it found hierarchs who supported its stances. And if the Eparchial Synod is really the highest body, then regardless of whether its decisions are right or wrong, its "synod-topped" structure of administration might let it override any decision taken by an "orthodox" Archdiocesan Council.
So the next question becomes what would happen if an "orthodox" Archdiocesan Council was in opposition to an Eparchial Synod. Based on what
FULK NERA wrote below, it appears that the Eparchial Synod could always override GOARCH's Archdiocesan Council:
In that case, if the issue was important enough, Greek parishes would want to leave GOARCH like Episcopalian Churches left the EC USA. In that case, who owns GOARCH parishes' property? GOARCH's recent Supreme Court brief is making a circuitous argument that GOARCH's leadership owns all its parishes' property because the property is for the purpose of following Greek Orthodoxy, and because supposedly only GOARCH's leadership and not secular courts decide whether parishes are following Greek Orthodoxy. I haven't studied the issue deeply enough, but it seems to me that GOARCH needs to have some regulation specifying that GOARCH owns all property if that is what GOARCH wants, instead of GOARCH just relying on this circuitous argument to claim ownership.