After finishing most of my Path of Ascension achievements on my demon hunter, I swapped to my paladin but couldn’t buy any transmog because the achievements are not account-wide.
Seeing as your class or armour type has no effect on the gameplay since you do them as Pelagos, Kleia and Mikanos, this feels a bit overkill to do the achievements like Master of the Path or Disciple of Humility 3 more times over for each Cloth, Mail and Plate.
Please make these account-wide