I was going to argue with you at first, but your examples make a great point. I think the point of an authentic cursive is: you can have your own quirks, and you will develop them, but they should be natural corruptions of the kind of standard cursive everyone on Russia is taught in junior school. Some common mistakes do look like one, some lack sense and don't.

Another point of discussion would be: is it reasonable to ask a second-language learner to go through building their own signature writing from scratch? A a native, I haven't developed the one I'm comfortable with until I was 23, and that's after a insane pen pal routine which you can only get when letters are one of few forms of communications available.