I'd be happy to work on the lead (or for anyone else to have a go at it), and any suggestions for improvement are always welcome, but it seems absurd for an FA not to have an FA class rating from a related project.  Basically, you're saying your standards are different from community consensus as determined through the FAC (and, in this case, FAR) processes. The two ratings in the mathematics project's grading scheme that are not subjective are FA and GA.  In this case, rather than attempt to unilaterally downgrade the article I think a better approach might have been to raise the issues you see on the talk page (or simply fix them).  In the future if you're hesitant to "sign" an FA or GA rating, then perhaps you should add the rating but not sign it.  Of course, if the mathematics project wants to have its own "FA" sort of rating, that's fine, but then it shouldn't be called FA and shouldn't link to WP:FA. 

On a perhaps related note, I don't know how many participants from the mathematics project actively watch Monty Hall problem.  It is a fairly difficult article to maintain since it has both the same sort of problem as 0.999... (i.e. many people simply disagree with the mathematically correct conclusion) and the additional problem of being a simple enough problem that everyone has an opinion.  I'd welcome help maintaining this article from you and anyone else in the mathematics project.   Rick Block (talk)