I have a monk with a vastly outdated Inna's set, which is still extremely viable.
It makes you wonder how people played RPGs, back before somebody just linked a "build" on websites...
Figure things out? You have to actively try pretty damn hard to gimp yourself entirely. The only thing that you'll ever really have to absolutely min/max for, is the higher levels of Torment. Spend some time, learn all the new skills/runes and how they interact, grab some drops, and worry about the most efficient builds once you've gotten used to the game(seriously, quite a bit has changed, especially if you haven't played since release). As most people have been saying, a lot of the skills are pretty well balanced now, to where a lot of stuff comes down to preference/playstyle(which is how it should be). Besides, a lot of the new legendary items make "the new hotness" change in an instant.