On one side, this feels bad because you want to avoid playing the game until next week. And then next week. And the week after that.
On the other side, grinding is terrible gameplay and it should never be incentivized.
These sorts of problems are largely unavoidable in any kind of infinite progression system. And that's why infinite progression is bad. Every artifact level should cost the exact same amount of AP, and the maximum level should be capped at (say) 20. And then when 8.1 comes out with new content, increase the cap to 40. And so on. The idea being that if grind it out quick, it'll take 40 hours to max-out the necklace. And if you do time-gated stuff like emissaries and weekly IEs, it'll take 20 hours. And when you're done, you're done, until the next major patch.