Partial answers are preferable to answers posing as comments.
You have already identified the common reason (other than lack of time, which is surely temporary) why some members post answers in the comments section:
Many expert users here avoid posting them in the answer box fearing that they'll have to defend their answer.
This is the other recent ELU meta question on this topic that OP has so subtly referenced with a tiny footnote:
Is SE enforcing "no answers in comments"?
This extract from the truly excellent, highly upvoted and accepted answer by @Meta Ed is very pertinent here:
There is no new initiative to eliminate answers in comment. They have always been discouraged.
The purpose of Stack Exchange is to get expert, peer-reviewed answers to good questions out on search engines for the benefit of the asker and anyone else with a similar question. Answers in comments cannot be downvoted. Lacking full peer review, they are are really not so helpful to the author as you might think (...)
Comments are truly local and transient. So an answer in comment might never help anybody else. This is why Robert Cartaino objected to the answers in comment on the post you linked.
The unsuitability of writing answers as comments has been well explained all over Stack Exchange and especially well recently by Director of Community Development @Robert Cartaino while dealing strictly with several instances on Interpersonal.SE where OP @NVZ is a top user and (unofficial but very helpful) community moderator:
<comments removed> If you have an answer, please post it below. Comments do not have the feature to properly vet whatever you say here so without activity like proper voting and wiki-style editing of content, answering here defeats the purpose of having this Stack Exchange site. – Robert Cartaino♦ Aug 3 at 13:43
Related meta threads on IPS.SE:
Please note I am referencing these threads here not because I think that the way comments are treated at IPS.SE is somehow directly related to ELU, but simply because IPS is the only other SE site where I am really active, after ELU, and because I understood that all those points about posting answers as comments are equally applicable to all SE sites though we seem to have evolved our own conventions about it here at ELU.
The main point that was made in those discussions is that an answer posted as a comment cannot be properly peer-reviewed, and can also disappear anytime. Robert Cartaino deleted many such comments on IPS.SE with full justification and thus educated that community to write answers as answers and not as comments. So I myself never post answers as comments anywhere on the SE network.
Moreover I have requested many members to write up their comments as answers while reminding them that a comment that reads like an answer can get deleted, and most of them graciously re-posted the comment as a well-developed answer, especially on Interpersonal.SE and Politics.SE but also here on ELU.
In short, SE says that posting an answer as a comment should not be tolerated, and I think it is implicit that senior members at ELU can claim no exemption to this network-wide recommendation.
Some ELU members' reasoning that "some questions are going to be closed and do not deserve a proper answer but we are willing to help OP by writing a brief answer as an explanatory comment" is even more perplexing. I just cannot understand that logic. Don't ask me to discuss this further here but many senior members have reacted thus while explaining why they posted a comment answering an apparently close-worthy question.
@NVZ's suggestion to post your 'idea' or 'unreferenced answer' as a community wiki is certainly well-made and we should seriously consider doing that when we are tempted to leave an answer in a comment.
But if a member cannot be bothered, then moderators should not hesitate to delete that answer posing as a comment.