New to Season 4, the Hero Track no longer requires Aspect Crests and you only need Wyrm Crests to hit Hero 6/6.
If you have a Hero Track piece and go to the upgrade Vendor, you'll notice that for Rank 5 and Rank 6, you only need Wyrm's Awakened Crest.
Compared to previous Seasons, Rank 5 and 6 required Aspect Crests. This means that without stepping into Mythic or keys higher than a +5, you can get gear up to 522 item level!
It's unclear if this is a bug or not.