Agreed. It’s not exactly a unique spec defining aspect anymore. Fury has had access to it for quite a few expansions, it was sidelined initially for Odyn’s Fury but then brought back in with the advent of Hero Trees.
Lore wise there isn’t really much differentiation for the most part. Media wise there are Dual Wielding Samurai/Swordmasters which were the initial inspiration for said archetype in other media.
That’s just the crux of it for the most part Slayer is basically just the aspects of Blademaster that are unique to warrior and renamed as such as certain utility they did not want to provide to us which is fair enough in itself. Windwalk and it’s stealth component and the Mirror images and their micromanagement weren’t exactly on theme for WoW’s Warrior.
Slaying Strike should’ve spawned an after image that cycles between different animations at random of a jump slash, horizontal slash, diagonal slash to strike your target though instead of it’s current weird sideways stab animation.
Honestly though WoW’s animation dept needs a shake up for Melee to have different animations for Swords, Axes/Maces and Polearm/Staff since they’re different fighting styles, I’d even go as far as changing up the combat ready stances to be based on weapons equipped and not races because let’s be honest some of the stances look awful with some weapon types and don’t quite make sense from a thematic pov. But that’s another rant entirely.