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The main factor in this argument is still what kind of team the move is being used for. For a team that needs hazards gone no matter what, Defog is the better option, pretty much guaranteeing to get rid of hazards. If the team lacks a glaring weakness to rocks, either is fine. Of course, if you...
Trying to find a 5 IV Adamant Timburr with egg moves Drain Punch and Mach Punch and gen V move tutor moves Ice Punch and Knock Off. Would be willing to trade 2 Pokes for it.
Also looking for Impish Vullaby with Overcoat, Knock Off, and Foul Play.
Stealth Rocks were not incorporated into the metagame specifically with Talonflame in mind. Similarly, most people don't pack Fire Blast and the like simply to hit Aegislash.
On the other hand, the closest things we have to counters regarding Mega Lucario are generally things specifically...
Regarding the bullet points on Mega Lucario:
1. This is just outright untrue. Finding out what set it's running generally requires taking a good chunk of damage if not outright sacrificing something. They won't always go for their setup move first turn as they often don't even need it. There are...
The Mega Lucario aspect of this has already run its course, it seems. While I do feel that his vulnerability to revenge killing should be considered as more of a factor by the pro-ban side (this is being treated like a complete non-factor), it still wouldn't be reason enough to justify him...
It seems most people are focusing on the physical variant. If you take the special set into account, that leaves even less options to deal with Mega Lucario.
A common theme that seems to be making itself clear is that almost every counter/check has a weakness to Stealth Rocks. Essentially...