You are correct. Left justified text was the de-facto standard. That's primarily because, when drafting on the board, we didn't have a computer to work out all of the spacing for us and writing backwards was a pain.
I once worked on a project, a large piping plan, where a lot of the text had to be right justified (picky customer). My head hurt after working on that thing for just a couple of hours. It's just not natural for us to write that way and your brain has to wrap itself around the concept.
Then, computers came along and made a task like right-justified text not only easy, but the default method for leaders and what-not. Does that make it better? Not to me. I started out drafting with CaveCAD (i.e. a pencil, a board, an eraser and various triangles, etc...) so I got used to seeing everything left justified. When I look at right-justified text it just looks ugly.
That doesn't make it wrong, though. The fact that it is the default justification for things like leader text flowing to the left... and that most users don't know how to make left-justified text in that situation, I tend to just accept it and overlook it.
Of course, my users can't figure out the basics of OSNAP so maybe I've just learned to accept and expect less from them.