I have a follow up on this if you can help me understand. What about alts when you’re done? Do you have to play through all the acts? Or even that beginning part until you get your mastery? Everytime?
If you're playing multiplayer, you can get carried and level anywhere in the game by portaling to a friend and playing with them.
If you're playing alone or doing it "legit" so to speak, you can use dungeon keys to skip sections of the campaign. As we add more dungeons, there will be more skips that you can combine in different ways to customize your leveling experience.
Either way, you'll still need to complete a set of passive and idol quests to get full power on your character. There are more quests that have these rewards than rewards you can get so you don't have to do them all. This means you can customize which you pick and cater the questing experience to what you like.