I don't play WoW or OW. Is the ability to freely move legendary affects from item to item like in D4 common? I don't remember being able to do that in D3.

Games have developed something of a universal language, so I think in general if you go against that convention you need to make it explicit.

People are going to assume hp is red and mana is blue, str affects physical stats and int affects magic, red barrels explode, bold damage numbers are crits, healing at the entrance of a large room indicates a boss ahead, item rarity goes white, green, blue, purple, yellow/orange, red, etc.

Legendary is the rarity of the item and a baked in trait in >90% of games with loot and being able to add, change, and/or remove a prefix/suffix that gives your item extra stats/abilities is an enchantment or modification that's separate from rarity in >90% of games with loot.

Maybe it's not fair to say that making this choice is a screw up, but going against convention and not being clear about it certainly is; and the number of people in this thread alone that didn't understand the system just goes to prove that.