To use the most efficient build, he needs the items to support it.
Since OP is new to the game, and asks starter questions here, it shows he has no "friends" that play the game.
Suggesting he should get powerlevelled is the worst thing you can do: he will have to find someone to level him (taking away actualy playtime), he would miss out on the story and the feeling of progression, he will not have items at level 70, he will not learn anything about the game mechanics and will have to become a leecher to get his items (taking away the fun again).
On top of this, depending on what you are doing, the most efficient build is difference: rifts/bounties/low grifts are based around maximum speed, high grifts are based around maximum damage stacking and controlling the mobs.
Once you have the set, basically any build goes for T6. Before you have the set, you build around the items you have and the skills you enjoy. As long as you are not pushing for the high ranks, the most efficient build will always be the one you enjoy the most, as it will allow you to actually play instead of feeling like work
I never suggested he be powerlevelled. I stated that the best builds are best for a reason (and there are several best builds that are itemization agnostic depending on class).
Also you state that Grifts are about max damage and enemy control. That's just a fancy way of saying maximum speed and some degree of experience.