Yes. It’s aesthetically unpleasing and many times confusing to a point that I find myself not even bothering to attempt to read posts that aren’t quoted in one of the two normal formats (i.e. html blockquote or indenting).
I address point by point virtually all the time. I use the blockquote and proper spacing to make the post as graphically pleasing as possible. Have a look at how this is done in this post, and the rest of that thread. Try to imagine how that discussion would have looked if the parties did not quote properly like that. It would have been virtually unreadable.