When I had very little reputation on Stack Overflow and I wanted to comment a clarification to somebody else's answer, I wrote a bad quality "answer" that had my comment in it, which would then be picked up by the script and turned automatically into a comment. Should this be fixed to completely prevent people with low reputation from commenting or should it remain?
To answer the question in your title - Yes, auto-converting low-quality answers into comments can technically be used by low-rep users to write comments. They can also 'use' a moderator's ability to convert short answers into comments to write comments.
This is not a bug - it is a feature of the site that allows users who would otherwise be posting low-quality answers to contribute comments. It also isn't exactly a 'workaround' to prevent low-quality comments, as moderators can still remove problematic comments and opt to delete answers before they become comments in the first place.
In short, yes it CAN be used that way, but in part it is supposed to work that way, and any abuse that results from it working that way can easily be fixed.