I totally agree with your post. Like you, I’m concerned about many aspect of a Legendary items define your build orientation. I’m concerned that those Legendary will become completely mandatory for even starting to play the build you want. And that I’m forced to use all the designed item for that specific build, like the Sorceress Teleport build in the Blizzcon Panel. You MUST equip all the designed item to play that build, that’s it. So it feels exactly like current Diablo 3 set’s design. You must play alternative build until you gather all the Legendary items. I think it might completely kill diversity and creative build. But for the moment, that’s theorical because we didn’t get any info on that since a while and maybe they changed some stuff. Like buffing that oversimplified Talent skill tree.
I talk about that in one of my post. (Middle of the post) and I also explain why I prefer a system based on the Skill itself