Very true but for design work you would manually have to keep updating these. Hence some of the issues we get from engineers with things not always matching.
This is a good example where the math function in smart text could come into play because you could use a combination or "-" and "<" or ">" to create an arrow for direction "<-" or "->" than you could use if/than statements to change which <> to use and delineate the direction of the slope.