I have a forum for about a year now, and my users are still confused about the comment-to-replies option. I think this is caused by two issues:
The comments are formatted almost the same as the replies. The only difference is a slight indention - which I like, but still, in a long line of replies it kind of gets lost. Perhaps making the comment's font significantly smaller than the replies would be extremely helpful and improve the readability. Especially when the post is a question.
I think the option to comment on a comment is really confusing as well and I would like it if that option was disabled.
See for example Stackoverflow where the comments on replies are in a much smaller font. Also they have eliminated the line that shows the User and so it takes up less space than the ansnwer and makes it easier to scroll through. I like that.
By the way, thanks to the team for all the awesome features and the design! We are really enjoying our time with you 😊