I think it’s important to create topics which allow people to contribute meaningfully to a discussion, rather than ones which try to cover too much ground.
For instance, this topic is a mixture of several different elements all introduced in the OP which I don’t think allows anyone to contribute to any of them fully. It’s a community topic, but which appears to be floating the idea of a new feature for flagging. Though the quoted text is concerning an agreed/disagreed flag score which doesn’t seem connected to that [1]. It also goes on to criticise a moderation decision on the site. And because the replies are interwoven with a little of each within the same posts, it’s also impossible to split out or bring back on-topic in any meaningful way. 
I think when creating a topic, it’s important to decide what you want it to be about, as a topic can’t be about all things at once without leading to a fractured and ultimately unproductive conversation.
Obviously, all sites are different and may have different approaches to this, and should be free to do so. 
We tend to make our decisions as a team here on Meta. 
As for the feature request itself, I think you have to trust your admins and mods to make the right choices. They do have a good sense of what is or isn’t expected, and will often work as a team to achieve this. There’s also some good reports on the dashboard you can use as oversight too, depending on the size of your team (or you can create bespoke ones if you have the data explorer if they don’t suit).
So, what do we do with this topic? Recategorise and retitle it to properly reflect what it’s about? There doesn’t seem to be an obvious choice for that. There also doesn’t seem to be a good split point for making it two (or more topics). Or do we close it and encourage the feature to be made into a feature topic and the ux into a ux topic, and draw a line under the fact that sometimes topics need to be closed at a moderator’s discretion to handle these situations?
(and which, slightly tangentially, already exists. Though recently downplayed in the flag UI as we didn’t think anyone was using it. Potentially a good ux review-queue topic
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