There isn't really much of an advantage to grinding the artifact xp vs. progressing through Legion the way you pretty much have to. And make no mistake, you have to progress through Legion by questing through the zones. Don't try grinding out dungeons to 110 or finding fast-spawning 2-shottables to level. Legion is utterly linear in its progression structure. You MUST do the quests to get the artifact power and you MUST do the quests to gain rep with each faction to eventually unlock world quests, which are the chief means of gaining artifact power beyond artifact level 10 or so.