One other thing I've noticed is that most of the older builds that achieved Legendary / Mythic status based on gameplay alone had discovered new quirks in the game, or new combinations of abilities and fully exploited them.
Now that the game has been out for so long, and most of the unique twists on the gameplay have already been discovered, it's getting more difficult to create a build that really stands on its own based on unique gameplay alone. So the roleplay aspect, equipment combinations, etc., really go a long way towards differentiating what is essentially the same build as others that are already out there.
A recent example of this is Henson's Ceya-Tar. If you look at only the gameplay, it's really just a standard sneak archer using illusion spells with a bound bow instead of a smithed one. Yet the build was very well received because of the strong lore and roleplay elements that help differentiate it from being just another sneak archer. It "feels" fresh as a result, even though it's not really all that different.