I would answer this as follows:
Based on TRiG's comment that one is not expected to be an expert in another religion than ones own.
These questions should be off-topic if:
- The question doesn't offer a good basis for comparison:
Let's say we want to compare a kind of worship between Islam and religion X, but OP didn't describe how this worship is handled in religion X.
- if the questions is not focused enough.
Note that any answer primarily will be based on the information and details given by OP, so one should be clear that any wrong information in the question post may imply a wrong comparison, unless the person answering has enough background knowledge of the religion compared with! And it primarily will -hopefully- be based on the Muslim perspective.
Else the question would either be considered as unclear or too broad (other closure-reasons can't be excluded).
The question is on-topic as long as we have a basis of comparison.
Like a comparison of specific concepts:
How is the concept of Reincarnation treated in Islam? or Does Islam believe in rebirth??
one could also add this one asking about an equivalent of a concept:
Is there any Islamic equivalent of Khumra (with examples)
But of course the fact that many of these questions may lead to answers which will represent the Muslim perspective (Only) and hardly be fairly representing opposite views may lead to a case by case judgement (as preaching the truth shouldn't be the goal of this site).