I mean, if you want to play at range logically you choose a long range skill set. Filling the traits with whatever skills that have synergy with your goals.
For example, I want to play a rifle Warrior. Well, I am not going to equip a greatsword & 2x axes. Naturally. I am going to get a rifle, pick rifle traits and so on. There might be this or that trait a tiny bit better than say, extra crits on full rage. But "it doesn't matter/play what you want" applies still- it doesn't matter too much. I can play what I want as a rifle Warrior provided I am logically pursing my goal: using a rifle at range.
If I want to make a defensive build, I am not going to select 8 offensive skills and 9 offensive traits. Though it's highly doubtful I am going to fail or be seriously effected by choosing a stability defensive skill over a stun break defensive skill.
I can't think of a single thing in GW2 PVE that isn't easily understood or practically workable.