Comments have long been a battleground on this site. Some members are very attached to this mode for all types of communication. We've even had long-time users ragequit over having a comment deleted.
My theory is that some people become used to the chat room discussions or are generally adapted to texting, and so using the comment box feels conversational, inclusive, friendly, and informal. And who wouldn't like to have a friendly chat about a topic of interest? Especially because if we're chatting about it, nobody needs to do the hard work of posting fleshed out research.
The fact is, however, that comments defeat the purpose of the question and answer format because the site itself was designed for people to read a question and then the various answers to it. A transcript of a discussion in the comments makes it nearly impossible to figure out the nuances of the various suggestions and sidebars.
Part of the trouble is that we have long-term users who don't want to put a lot of effort into answering the kinds of questions we get these days, but do want to continue contributing to the site. Unfortunately, they don't seem to understand the harm they do. They set a bad example for others as many askers feel satisfied by the comment discussion. They've gotten their answer except that now we have "answers" that cannot be community improved, cannot be community edited, cannot be community up- or downvoted upon, and cannot be pulled out from the rest by an Accepted mark.
They become sadly orphaned questions left in the Unanswered section of the site.
So with that in mind, here are your questions again:
- How is it objectively determined when a comment is an answer "in disguise" and not just a clarifying comment?
It's not "objectively" determined, since actual people are doing the work. However, generally "Will X word work?" or "Why doesn't X word fit?" would be an answer in disguise. "This is the answer to your question" is also a good indicator that it's an answer in a comment. Additionally, we also remove comments that are requests for clarification when the post has been edited to provide that clarification, and we also remove clarifying comments when the clarification has been edited into the post.
- Why are questions being locked rather than the comments (which are always considered ephemeral anyway) simply deleted?
Have you ever been on the open ocean with a hole in your boat and a very small bucket?
- If a question has been voted to be closed, why has the community sentiment of still being able to say something in the comments to help the questioner been ignored?
I don't understand what you are asking here. The question is not closed.
- Despite protestations to the contrary, why has this behaviour of locking questions for comment answers suddenly been introduced? I have only seen this being done by one moderator, only in the past couple of weeks, and also in an inconsistent manner. This is not something that has occurred on any kind of regular basis in the past several years at all.
You have only seen it recently because we have had the ability to do so only for a short period of time. You've seen it done by one moderator because there's just a few of us and he's the one here most often. He has the full support of the other moderators. It may seem sporadic and inconsistent to you, but we have to direct our efforts to maximum effect, so it's applied to questions that are Hot Network Questions or may become so, and generally also single word requests, and also questions where many members are offering answers in the comments.
It would be beneficial if users who no longer wish to answer but still wish to contribute spent time spiffing up existing questions and answers rather than commenting. Save that for the chat room.