So first things first, I've watched the replay and I think you got a good strategy going on here. I agree with the Weakness Policy since Onix has a lot of weaknesses, and Sturdy is definitely great to help raise Spd. after starting off with the move Rock Polish.
Personally, I think that Onix is the best choice for this LC strategy because he is able to withstand an attack with it's Def, otherwise hold on with Sturdy if hit by a Sp. Atk move; thus ensuring that he's always able to move with Rock Polish.
When looking at your moves, I think that Explosion is unnecessary. I like Earthquake and Stone Edge, but you may want to replace Explosion with maybe Iron Tail. Stealth Rock and other status moves are OK, but the likeliness of Onix fainting will be close to certain, after following it with Rock Polish. So, if you do decide to use Stealth Rock, maybe have another Pokemon in your team that knows it.
Also with your EV's, I think you should max Atk and Spd Ev's, and not HP. The reason is, you already have Sturdy, so you should withstand the attack anyways. Having 252 Ev's in Spd and Atk will definitely make it more unstoppable.
That being said, everything else looks fine. Your Choice! Hope I helped! :)