It’s just not worth playing an alt at this point other than leveling (and that assumes using group content to get carried when an alt’s power is so far behind in the 60s and 70s).
Maybe they will fix the issue with artifacts / gear being so behind on alts, and if we are lucky, add some benefit to power / gearing for alts.
But right now alts don’t gain anything in the way of catch-up for gear or power and just get further and further behind as they approach and hit 80.
Oh and I love that my alt’s dailies are all crap like run a specific mythic dungeon, heroic raid, heroic world when they have terrible way behind gear that would suit a level 50 character while my main gets stuff like complete a normal dungeon.