Well the way I see it, you don't have to remove the line tool, but it just gives you a quick reference button that works better than fidgeting with the line forever. Then you can use the line for critical information (some information will be color coded.)
As for the mention of height, it should be on a way point basis, so the height should already be factored in and things color coded to help know if there is a reverse slope, blocked LoS, and such. Yeah it isn't going to be perfect but it'll save a lot of time.
As for realism and "over the top" complaints, there is a LOT of things that are abstracted in this game. If you like pure line LoS, you could just turn it off or perhaps choose a difficult setting (like Iron I think it was where spotting included your own squads) which will automatically strip this tool.
With a new engine or engine enhancements, they could try to bypass the old technical limitations if they put their mind to it I think.