To PAA: I’m not sure how many more achronimrishonim the MB ‘invented’ to count much more than the Shach or Pri Megadim or the Graz in the Kuntres Acharon. Also being that they were not Rabonim (the PRi Megadim and Shach) I’m sure we should not follow them for their Hachra (I don’t think I have ever seen ???? on them). As per the MB not being popular in Europe if you go through the Kol Kisvey of the CC you will see that he was asked for thousands of copies for in Europe America and England (they printed the receipts and if you look in the Meir Einey Yisrael 6th vol they have other unprinted letters to the same extent). While in the Kol Kisvey of the OH there are two letters asking for his sefarim both from Russia.
As for the GR”As popularity it probably was his own, but if you look at the Hakdama to the Chayay Adom you will see it was him or previously. I think most of this is a review from before.
To Daniel: Its all very nice what you wrote except that for a Bar Mitzva Bochur I think the MB is the worst sefer to learn better go with a Kitzur or Chayey Adom. Maybe this can be a new thread on how to learn the MB; difference between the MB BH and the SHar Hatzhion and which Simanim did he not write.