I say we should keep it
It's a good way to describe what you are asking about and if the people can't narrow the scope of their question down enough than it's not the fault of the tag. I wouldn't want to miss alternate-history questions just because people were not able to take a tag and then focus on an aspect like they are supposed to do.
All tags are too broad. That's because they are tags and supposed to group different kinds of questions together. To take some numbers from a comment from Michael Kjörling:
That means roughly 31% closure rate. Pretty high, but let's look at some other tags. Like magic.
That makes for roughly 34%. That's a bit more than alternate-history.
How about aliens?
That makes for roughly 26%. Not where alternate-history is, but still quite a lot and pretty close.
I think those numbers are high. And it would be good if they were not that high. But something around 30% closure rate is no reason to ban a tag and thereby discourage people from asking about these topics.
Maybe we should think about making the rules more specific by stating them in the tag excerpts. For example currently the tag excerpt from alternate-history reads:
For questions that ask what might have happened if history had taken a different path.
The tag wiki on the other hand specifies among others:
These questions often fall in the "What if ... ?" category and are at risk of being too broad. When asking the question, people should focus on only one or a small amount of aspects.
By mentioning that people should only focus on one single aspect we might reduce the numbers a bit. But we will probably never reduce them to something like 10%. People will misuse the tag like they misuse any other tag on the site. The difference between alternate-history and other existing tags is not that big that we need to intervene immediately and especially not by removing the tag altogether.
Granted, my examples are on the often-closed end of the scale and a lot of other tags are far below these numbers. But I don't think that the numbers should be the sole reason to get rid of the tag.
About your comment at the end: I think closing questions fast is a good thing so that people don't answer stuff that will get changed. New users often don't ask clear questions or have a clear idea about what they need to know and what they need to communicate for that. It's important to state how the OP can improve his post and mention that you are voting to put it on hold until those edits are made to improve the quality of the answers you will receive or something along those lines.
But this is getting a bit of off-topic and might warrant (another) Meta discussion like here or here or here.
