Scarlet sword & chest


Hey guys,
I love that we are finally able to obtain legendary items by regular way (meaning not just by lotery).
I just have a question to ask: how can we improve skills of sword or chest?
Is it intentionally different skill than any other item in game so we can’t improve it? (making the sword weaker than unique weapons…)
Only way to improve skill level of these 2 is using potions from challenge which grant 100% chance to improve skill level. But even those are pretty rare and only obtainable this challenge as far as I know.
I suppose this is intentional. Or is there something I am not seeing?