Campaign is a thing to be endured, preferably only once.
Unless they've changed the difficulties and xp rewards, do adventure mode on hard to start, skip expert to master once you're better geared but still able to kill QUICKLY AND EFFICIENTLY (taking time to kill shit on scrub levels out of some misplaced notion of I'VE GOT SKILLZ is dumb), then once you've got the first two pieces of your season reward set (I assume you're playing in a season, but they might not be available on consoles yet) up it to Torment I-II depending on what you're able to handle.
Grind. Grind some more. Grind a whole lot more. Grind, grind, grind. If grinding rifts and greater rifts for incremental upgrades is not appealing to you, this is not the game for you. I really can't stress that enough.