How does a downvote with no comments assist in shaping a great answer and contributing toward the aims of this site?
It's clear and direct feedback that (in the opinion of the voter) you're doing something wrong! Receiving enough of them should cause you to reflect on why you've missed the approval of the community with your post. Of course a comment or two could be a helpful part of the process, but considering (from the tour) the aims of this site include -
We're a little bit different from other sites. Here's how:
Ask questions, get answers, no distractions
This site is all about getting answers. It's not a discussion forum. There's no chit-chat. (emphasis added)
Comments can actually work against those aims by distracting and provoking discussion/chit-chat. The onus is on the OP to write a good post, not the readers to write it for them nor should they need to invest time in guiding them to do so. If they do in fact do that, it is a courtesy for them to do it.
You seem to be hung up on this issue, and I think the main reason is that you've mistaken the purpose of the voting system.
Votes are not primarily a feedback mechanism. In other words they are not primarily for you as a post author. If it was, you would have a point that it isn't optimized for that. But it's not. It's a signal you can use, but it's really for something else and the way it functions is for that other purpose.
The primary purpose of voting is to sort answers and signal site readers about the relative value of answers. It's a crowd-sourced sorting system amalgamating any number of factors about perceived relative usefulness, accuracy, etc. For various reason (that you should research on [meta.se]) for that to function properly the votes themselves need to be anonymous and are therefore strictly not correlated to other mechanisms such as commenting.
Votes are not meant primarily for you as a way to improve your answers. They are for everybody else. They further the aims of this site in that new visitors to a question find the best answer as ranked by the community at the top of the answer stack and less well received ones lower down.
Another reason why downvoting without comment contributes to the aims of this (and all SE) site is something I touched on in my answer to your other question:
Voting is already low across every established SE site that I follow.
Voting - up and down - is extremely important to the way SE works. The idea is that if lots of people vote, then the relative vote counts are a very good indicator of how good or bad an answer (or question).
Every site I'm active on has meta-discussions every now and then about how little voting there is, so an additional barrier to voting would actually hurt the aims of the site.