The passive skill tree could add actual complexity to the game. There is no exact build like WoW or D2.
If I give you a choice of 100 things and told everyone that they could have 20 of those things, eventually everyone will agree on which 20 things are the best out of the 100 and start picking just those things.
Welcome to theorycrafting.
Not really no.
A bunch of people make take those best things to just have, but many more will take other things just for the sake of having them...
Suppose their is an optimal witch build in PoE for extreme devestation.. most everybody makes that build for farming or team play or whatever..
This next thing I can tell you with 100% certainty.. the vast majority of people who make those builds would NOT just stick to that build. There would be other characters/classes made that may be unique, goofy, ridiculous, or they might find a hidden gem. Fact is, they will be made.
So you can't sit there and say that everyone will agree on what 20 things are best, or what builds are best or whats optimal. Everybody has different flavors of play, and that will be exercised.. not like a linear path like D3.
You can't tell me that I would stick to a cookie cutter build (because I wont), you can't tell the next person they will too (because they probably won't). Hell, even yourself, how likely is it that your going to make and stick to only a cookie cutter build? Highly unlikely.
Complexity to the game