Is Mishna Berura the "Posek Acharon"?

I’m not sure where the idea started, but I’ve heard how the Mishna Berura is somehow the final authority in halacha from more than one talmid chochom. And I don’t understand it.

That’s not to say we should take the work lightly. Mishna Berura is a wonder of clear writing, scholarly coherence, and moral authority. But the last word in halacha? What would that even mean?

To my knowledge, for instance, chasidim, sefardim, religious Zionists, and Briskers never accepted its authority. And later poskim like R’ Moshe Feinstein and the ערוך השלחן weren’t hesitant to disagree when they felt it was appropriate. So exactly which Torah community is bound by this authority?

This has overtones of the strange but oft-repeated sentiment that “we’re all required to follow the psak of the Shulchan Aruch” - even though virtually every page of standard שולחן ערוך printings contains נושאי כלים openly disputing rulings of the מחבר or the רמ”א (and each other).

And that’s assuming the concept of a “psak” even exists. After all, the Maharal famously opposed the Shulchan Aruch in part because he held that every Jew is responsible for knowing Shas well enough to decide halacha for himself. There is, the way I understand the Maharal, no repository of universal halachic rulings waiting to be applied.

Besides all that, Mishna Berura is a deeply kabbalistic work, and it would be strange to claim that Jews (like me) who prefer to follow traditional pre-Tzfas Judaism are somehow forced to instead adopt hundreds of kabbalistic practices. By my incomplete count, Mishna Berura quotes Zohar explicitly in at least 38 different halachos, the Shela in 64, and Magid Mesharim in at least two. You can see all of those results here. But that’s ignoring the many times he quotes Zohar or the Ari indirectly through the Magen Avraham - sometimes by name but often not.

Some might say that Mishna Berura is simply enumerating kabbalistic minhagim rather than recommending that we observe them. I find that unconvincing. After all, there are literally thousands of minhagim out there that he didn’t quote. He’s obviously picking and choosing just those he feels his readers should observe.

That’s perfectly fine, of course. The Mishna Berura’s personal opinion is surely worthy of our attention. But to claim that it’s somehow binding on all Torah-loyal Jews? You’ve lost me.