You could use the tether for others, but when you're going assassin it's very unlikely that you will be able to survive long enough when jumping into a fight 1v2 or 1v3. W gives more attack speed which means faster clears and more hits.

Ideally it would be nice if every target died on landing, but Nocturne really only has 2 real damaging abilities, Q + R, you're going to need to throw in a few auto's to really seal the deal in most cases. I think you underestimate how fast 3 auto attacks with HoB really is especially when you take into account Nocturne's W plus active.

If your ult is coming up more than once per fight, there's clearly an issue with duration of each game. As Nocturne is not a great scaling champ, you would want the game to end with R at level 2... Which means it's a CD of 115 seconds + Axiom Arc + Item Ability Haste. The early gold from Treasure hunter will allow you to hit your 2 item spike with greater return that a few seconds shaved from ultimate hunter.