I'd appreciate an answer to my question
In theory it could be that a drawing can be used as a mashal for kav, the question is what's the point.
Are we understanding kav, or imagining what kav looks like.
One of the primary goals of the Alter Rebbe is להפשיט הדברים מגשמיותם, not just verses in Ezekiel but also phrases and words in kabala and chakira.
Most people when seeing a line, see a line, and not what it represents.
Such a bochur already has some kind of imagination about the kav based on the words in the maamar, be it a measuring stick, an author planning the plot of a book and it's fonts, a ray of light getting weaker or what have you. The point is to explain to him what the maamar means by the measuring stick, the decision of how to write your book etc.
Drawing a line will make his understanding of kav more megusham in the place of making it more mufshat.
Some people will not see the line, but what it represents.
Such a bochur was able to understand the point that was brought across by the meshalim in the maamar itself and doesn't need the line.
So while it might not be a crime, I don't see the point.
A mashpia has to realize that the bochur might not be seeing the line the way he does.
I had a few minutes so I wrote, I hope that I got my point across clearly.