That’s because you are trapped in D3 view of items as build-defining.
Remember that D4 has skills that have ranges, points to allocate and empower said skills.
Remember too that D4 has a talent tree besides those skill point choices and that at the moment is quite tiny or has no clear purpouse.
Shift those legendary-build-defining to talents that unlock the more you develop into a skill, with crosssynergies between some.
Now you have a build as it should be, the decisions made on your character through investing points, with the gear slots free to stack on dmg/defense/proc chances, no mandatory BiS strict gear as it is now. It could be a rare with +skills to the skills you are using, a legendary with big damage boosts, etc. Much more flexibility.
Comment here if you agree and for the devs to see it: [D4] The problem with legendary powers (and solution)