Yes I agree and I think Waka would agree that Low Slash does bring a LOT to the table, obviously a skilled player is going to use it for more than just another Maul proc.
That being said - it does not make up for the lack of utility relative to Mara's and PT's.
Stealth is not a utility in arenas.
Sap is not a utility in arenas. (initial burst is never successful against a good team.)
Taunts
Low Slash
Knockback
Thats about it. Single target slow is nothing special. WW is a great ability but requires far more skill/awareness to utilize than what it *should* take. The knockdown from stealth is negligible.
Shadows/Assassins are missing some utility in competitive group arenas.
Shadows/Assassins mobility is lacking compared to Warriors and PT's.
With that being said - pull should be baseline ability for sins/shadows.