הלכות ממרים פ''ב ה''א ב''ד הגדול שדרשו באחת מן המידות כפי מה שנראה בעיניהם שהדין כך ודנו דין ועמד אחריהם ב''ד אחר לסתור אותו ה''ז סותר ודן כפי מה שנראה בעיניו שנאמר אל השופט אשר יהיה בימים ההם אינך חייב ללכת אלא אחר ב''ד שבדורך.
הלכה ב' ב''ד גזרו גזירה או תקנו תקנה והנהיגו מנהג ופשט הדבר בכל ישראל [ראב''ד-לא אפילו אליהו וב''ד הואיל ופשט איסורן בכל ישראל כדאיתא בע''ז] ועמד אחריהם ב''ד אחר ובקש לבטל דברי הראשונים ולעקור אותה התקנה ואותה הגזרה ואותו המנהג אינו יכול עד שיהיה גדול מן הראשונים בחכמה ובמנין

הלכה ג' בד''א בדברים שלא אסרו אותן כדי לעשות סייג לתורה כשאר דיני התורה אבל דברים שראו ב''ד לגזור ולאסור לעשות סייג אם פשט איסורן בכל ישראל אין ב''ד גדול אחר יכול לעקרן ולהתירן אפילו היה גדול
מן הראשונים
ראב''ד עיטור שוקי ירושלים בפירות קשיא עליו שהראשונים תקנוהו וריו''ח בן זכאי בטלה אחר החרבן מפני שנתבטל הטעם לראשונים ולא היה גדול כראשונים

It occurred to me that the ראב''ד is really saying something significant in the רמב''ם laws of הלכות ממרים פרק ב' הלכות א'-ג' . The thing that I noticed is that the רמב''ם's order goes  from most lenient to most strict. And the ראב''ד has the same thing but with the order moved two steps up.
What that means in plain עברית is this. To the רמב''ם the most lenient is things learned from the שלש עשרה מידות.  For that a later court can reverse the decision even if they are just a small court. The more strict level is  decrees of the sages. For that a later court can reverse the decree if it is greater in number an wisdom. The most strict level are גזירות תקנות ומנהגים made as a סייג to Torah that have been accepted. They can never be reversed. The ראב''ד's system starts with the last thing being the most lenient. He says that that ר. יוחנן בן זכאי reversed the decree to bring the ביכורים to ירושלים and not redeem them. The next level he explains in his comments on מסכת עדויות  where it says why are the words of the דעת היחיד recorded if the הלכה goes by the רוב? Because if a later court sees the words of the minority and agrees with them then it can change the decision if it is greater is number and wisdom.
The ראב''ד there says the later court would not reverse the decree unless the minority opinion was recorded. It comes out then that the later court can go against that majority because it is  a greater majority than the original court that ruled against the minority opinion.

Then the most strict is what is to the רמב''ם the middle level. That is decrees. There the ראב''ד says if it is נתפשט Then it can never be nullified.
Now you could say the ראב''ד is not disagreeing with the רמב''ם's division. But there is good reason to think that the ראב''ד is making the difference between הלכה ב and הלכה ג to be dependent on whether the decree has been accepted, not whether it is a fence to the Torah. You could argue this point  but for the time being let's just say that that is how the לחם משנה and רב שך both understand the ראב''ד.  That means that the ראב''ד is being strict in הלכה ב because as he says the decree was accepted in all Israel. That is why even a later court can not change the decree. And that means that in halacha 3 where the ראב''ד is the most lenient that is because the decree was no longer accepted.  I mean to say that certainly the decree was once accepted. But when ר. יוחנן בן זכאי came around an the Temple had been destroyed it no longer was the custom to bring first fruits to Jerusalem. So he nullified the decree though he was smaller in wisdom and in number.
Not only that but it would seem like the רמב''ם would have to agree that once the decree was no longer accepted,  it was no longer in force.  For to the רמב''ם how was it possible for ה to nullify a decree when he was smaller in wisdom and number? It was not a case of the 13 principles which is the only case the רמב''ם would have allowed such a thing.

That means that the ראב''ד and perhaps the רמב''ם also are thinking that decrees have force only in so far as they are accepted throughout all Israel. Once they are ignored they no longer have validity because the whole reason for their existence is gone.

So what comes out from all this is significant. That is that the ראב''ד is thinking slightly different from תוספות. What תוספות holds is numerous places is that if the reason for  a decree is nullified the decree itself is nullified. This is like רבה in ביצה page דף ה' ע''א. What you see from the ראב''ד is that what is determinant if if the decree is presently accepted throughout  all Israel. Not if it once was accepted.  ר. יוחנן בן זכאי certainly did not reverse a decree that had never been accepted.  Or which was based on the 13 principles. Rather it was a decree that had once been accepted  and then was ignored Thus ר. יוחנן בן זכאי could nullify it even though he was smaller in number and wisdom