That statement is incorrect. What is correct is that ranged builds with 6 or more ranger levels have lower dps (this statement is subject to change with each mod).
Your playstyle might affect your decision when picking a build. One great example of how playstyle should affect your decision is if you are a player that will often solo or duo quests then having 18 levels of ranger will give you the tools you need to do that easier.
Don't craft a radiance bow for your first greensteel bow. Radiance goes off on crits which is a rare thing when multishot is on timer.