TL;DR: While we could write a FAQ post on questions that are on-hold, I don't think we should make a canonical meta post with the contents you describe here, with the terminology you use here and use it for the reasons you describe here.
On this site, we get a lot of users who ask questions that are considered too subjective under our model. see revision 1
This one is not really true. Looking at the question closure statistics, most questions aren't too subjective, instead, they are not about Interpersonal Skills at all (off-topic) or are not detailed/clear enough to be answered (unclear/too broad).
Yes, pretty much. Specifically, closed as being too subjective.
We don't even have a reason to close question as 'too subjective', the closest one is probably called 'primarily opinion-based'. Turning the example that you picked from MSO into something only for those questions closed as primarily opinion-based would make such a post a lot less useful. The one on SO can be used for any kind of closed question, we should attempt to do the same.
Most of them are totally new users who discover our site via search engines (a good thing!) and assume that this site is just like one of the many other forum sites on the Internet (which more often than not, accept such subjective questions).
I'd like to point out that this is an assumption which is assuming those people are assuming this site is a forum. While it may be a logical conclusion, we don't have any data on it. Always be careful when doing this, you might offend people by assuming they assumed something, instead of thinking that they might have very well done their research and noted the difference. So we should not let a meta post on question closure reflect that.
I've seen some users rant externally about this site about having a bad experience, our community "not being inclusive enough", "considering my question bad", or "closing basic questions", when all they did was ask a question that would often be accepted on such a forum but was considered too subjective here.
People rant externally, and people are happy with IPS externally too. The post you link from on MSO is from 2014. I don't think it has done much to ameliorate question closures there: People still rant externally about having their question closed on SO. So please don't think having a FAQ post on closed questions would help remedy people mentioning their closed questions externally.
Secondly, as I said before, the question these people are complaining about wasn't too subjective, as there's no such close reason. Note that the MSO post also isn't focused on questions closed for just a single reason.
It could possibly also have a list of links to other alternative sites where they can get their issue addressed.
The only site I know that has such a list is RPG. And they have theirs in a separate post, not dumped in with the information on what it means when a question is on-hold. I also don't know if there are any respectable communities for IPS, similar to those RPG links. In my opinion, it doesn't help much to dump users on any other forum if it's not specifically about IPS.
Instead, we might better just have one because it's generally useful reference material for people, a thing we can point people to when they're asking a question on IPS that is closed (no matter for what reason) and they seem confused about it.
We should not make it about a specific reason for closure, and we should not combine it with a list of other forums, if there are any good forums on Interpersonal Skills out there, we might combine another FAQ entry like the one RPG has, but not dump it in with a post that generally outlines what it means when a question is on-hold.