There are a lot of people, myself included that rely on build guides for a lot of things like what synergizes with what. Especially in a brand new game where it’s all unknown to most of us.
The people that put these early guides together have the resources and knowledge from datamining and countless hours of beta gameplay and they have the best educated guess for what works.
If a pleb like myself just grabs whatever gear gets dropped and tries to build around that (like I did in closed beta) I end up with a character that is usually bad and struggles often making the experience not fun and some even move on to another game.