A few month ago I shared a possible solution where the suggested role for unique items is to create synergies between two different skills.
By that I mean that it would allow one skill to tap into the item powers / legendary powers of the second skill (and vice versa). For example: Rogue’s Rain of Arrows drop Caltrops instead of projectiles, or Druid’s Lightning Bolts are replaced by Raven passive attacks. Bonuses can stay intact.
I have examples in my linked thread above, and more (Rogue) stuff is collected here: Development 🏹 new Uniques for the Rogue class
The game has such abilities but I wish it would add them more consequently. This may do a lot for build variation, and seasonal updates could always serve at least 2 skills instead of a single one.