I understand ruebe has provided working code in his PBO above, I will be happy to answer if you have any questions to me. I made my routePoints manually though, using onMapSingleClick and manual labour.
Lines is blue is hopeless and rightly so as that was a super quick test of cutting edges by 30% - bad idea - bad result. Idea dropped.
Lines in green is not elegant we agree on that but it 'does the job' for now and I deem green route "usable" quality. My limited project time would be better utilized if I work on non-existant functions/features (as opposed improving beauty of lines on map). There is a chance I might revisit the code and try to improve one day but not today :)
BIS 'drawLine' function won't work for my requirements as the beauty of the final output is only one of the parameters and not the top one. drawLine is draw-once-lose-control-forever from what I read that's a no-go. In my project these lines I draw are bus routes and currently I am able to turn a given route to red color (i.e.: service disruption) at will as they are simply markers.
Should you -or anyone else for that matter- provide working Arma 3 code for drawing update-able Arma 3 lines with better support for curves I will be happy to switchover otherwise I will leave it as is -- I'll just go back and provide more position points resulting in finer map output.