The custom of Israel is law and small things.

Hello Rabbi, I read the article https://mikyab.net/posts/732/ and also heard the debate with Rabbi Chaim Navon
And I can say that your words are no less than the words of the living God, and may your springs be restored beyond the grave.
But when I explained the reasoning to my friends in the yeshiva, besides all the nonsense you mentioned that people say, they said something that I didn't find you responding to, which is that it is a rule in halacha that " the custom of Israel is law " and they tell me the same thing about several other such customs… Now, of course, personally, this argument does not convince me philosophically, but as a Jew who observes halacha, it is important for me to know how to respond to this argument. And why don't we say that just as we pray, even though we don't always agree with the simplicity of the prayer, but simply because it is the halacha? Why don't we say this in small details as well?
Thank you very much!