Arso:
“ You claim that the Lubavicher rebbe fits the Rambam’s criteria, one of which is Mashiach will be a king. So why didn’t anyone – not even the greatest of chassidim – recite the beracha one recites when seeing a king? The obvious, and only, answer is that they didn’t consider him a king, and for a very simple reason… he wasn’t.
Btw I believe that the expression מאן מלכי רבנן does not appear anywhere in Chazal. It is a paraphrasing of something said by an Amora in Gittin 62a, and according to that all Rabbonon are included. Nonetheless we do not find anyone, including the Amora who made the statement, reciting the beracha because even he did not mean that they had the actual status of kings. Proof being that Chazal say that a Rav can be mochel on has kavod but a king cannot. So clearly it is allegorical (that may be the wrong word, but you probably know what I mean).”
We definitely see the Rebbe as king in many ways- such as complete bitul to doing what the Rebbe says. Also, when a Rav pasken a something that creates reality, even if the world says something different.
Bar kochba definitely wasn’t annointed- there was no Sanhedrin then. But the Rambam calls him king, and candidate for Moshiach so you clearly see what kind of “king” the Rambam was referring to. (He wasn’t even accepted by most Rabbanim- so kvodo aino mochul didn’t apply there either.)