You also gotta see how the move is used and Vacuum Wave is the only move that can be spammed. it will be like Infernapes Mach Punch there is a reason it kept that move its a quick strike that it could always lead with. Aura Sphere is a Nuke not a quick strike move that it spams. If it became that it would look Weak instead of an Ultra Strong move.
There are plenty of moves that could function as that 'quick-attack'-type move. I agree that Vacuum Wave is kinda cool - and we haven't seen a Lucario really use that iirc. But it's a weak special-based Fighting-type move. And Aura Sphere is that as well - and the signature move of the Lucario species (and most associated with it). The 'nuke'-version is actually Focus Blast. Aura Sphere is pretty much the Flamethrower-level of the bunch (in between Ember and Fire Blast).
But really guys, Lucario's moveset is so vast that there's hardly a point in discussing it. I'd love Meteor Mash on Ash's since it hasn't been done yet, but between Maylene, Cameron, Korrina and Kukui there has been a lot of diversity.
Maylene: Metal Claw, Bone Rush and Force Palm, Aura Sphere
Cameron: Copycat, Circle Throw and Force Palm, Vacuum Wave -> Aura Sphere
Korinna: Power-up Punch, Metal Sound, Bone Rush, Aura Sphere (knew Swords Dance as well at one point).
Kukui: Close Combat, Dragon Pulse, Extreme Speed. No 4th move, but I guess we could guess what it would be.. xD
So pretty much EVERY Lucario has some unique move: Metal Claw, Copycat+Circle Throw, Power-up Punch+Metal Sound(+Swords Dance), and Kukui's was entirely unique.
Considering it's 'rivalry' with Farfetch'd, I'd argue that Bone Rush would be a great move for it to learn. Then both could get their 'Meteor'-moves: Meteor Mash and Meteor Assault.
- Vacuum Wave -> Aura Sphere
- Double Team
- Reversal -> Bone Rush
- Force Palm -> Metal Claw -> Meteor Mash
A mix from Maylene and Korrina. Cameron's Lucario pretty much still had a Riolu-moveset considering the circumstances and Kukui's was just weird and built to counter Naganadel.
As for the inevitable Sirfetch'd.. I think it's got Night Slash and Brutal Swing to kinda represent G-Farfetch'd 'Dark Knight'-ness compared to Sirfetch'd 'White Knight'-ness. I'm assuming Night Slash will be used to get 3 crits and will disappear afterwards. Brutal Swing might stay, but I don't even find that quite likely.
Sirfetch'd:
- Brutal Swing -> Meteor Assault: both are 'violent' or 'wild' swinging attacks).
- Night Slash -> Leaf Blade: Both are high crit-moves and the Grass-type is the 'purer'-version.
- Iron Defense: They've got to do something with the shield.
- Brave Bird OR
Dual Wingbeat.
These movesets differentiate the two Fighting-types by a lot. Lucario is the nimble sweeper and Sirfetch'd is the stocky whacker that needs opponents to come in close and get critical hits in.