If you think Artifact Challenge 6.1 to 6.3 is tough, just wait until you get to 7.3 to 7.5...Gaunlet, chestplate & boots 4* with HP(%) as the primary stat in Kaerok Castle on Hard or Brutal. Been on this for three days. Used a gazillion combos of 2, 3, and 4 champions.
Think you're pissed now? :(
And as a side note, Arena is just as bad...Been on the Mission of getting to first-level silver for four days now...Came close a few times, then lose 6 in a row. The Team Power of the team you're fighting is useless. The don't tell you about the 6 gazillion buff and debuff combos. Congratulatios! You have 44K and you've just lost to a team with 29K! Even though you have all four of your champions with 4-set and 2 set artifacts! Yeah! Let's play against Legendaries when you've only been playing for two weeks! :(