بسم الله الرحمن الرحیم
In the name of Allah the merciful the compassionate
I believe that you are assuming that the community is in agreement in having the proposed "Off-Topic reason" which is not accepted by the community and should be discussed at the very beginning, before doing any other things.
Then, when the community reached the consensus for having such an off-topic reason in this site, we'll find the one it should be replaced with.
So, I imagine that you are asking:
Do we need a new off topic reason for posts suspicious to be polemic?
To answer this question I should tell you that we need to define so some criteria to label a post as "polemic". As people from different Islamic school thoughts are active here we should deal with this issue very cautiously.
Knowing the above in mind we can't easily call the posts as polemic. On other hand, despite many of, if not most of, the existing issues between the two Islamic sects are really disputed, they are of the topics which has gathered the attentions from the scholars of the both sects. So, by stopping such posts, if they really exist, we are limiting the benefits of this site by putting a "keep out" sign for scholars and experts. Therefor, the number of hits to this site will decrease by having ordinary questions. So, by accepting this proposed rule we are stopping scholars and hence ordinary people from visiting the site.
Instead of this, I propose to devise schemes so that we can solve, or at least clarify, the disputed areas for the visitors. Of course both sects has it's own beliefs and possible answers for the so called disputed posts. Hence, we should teach active members how to act toward these posts instead of omitting the questions!