Nobody's countered this (admittedly weak) anti-ban argument yet, so I think this should be discussed.
"Aegislash has weaknesses to FOUR common attacking types - Ghost, Ground, Fire, and Dark!"
Has it occurred to anybody else that it might be the other way around - that the reason why those attacking types are common is BECAUSE of Aegislash?
Ghost - Ghost is arguably one of the best attacking types in OU right now. However, thanks to Aegislash's presence, most Ghosts have been pushed out of OU - not only because they can't switch into Aegislash's Shadow Ball, but also because the strong Dark type attacks (Pursuit, Sucker Punch, and Knock Off) that almost every offensive team is forced to run to deal with Aegislash also nukes them.
Ground - People have already brought up the issue of physical attacking mons being forced to run Earthquake, which is becoming a liability in OU thanks to the really powerful, really fast Flying types that are in the top tier of OU. Disregarding Aegislash, Ground is such a poor attacking type in OU - not only do you open up switch in opportunities to Charizard, Talonflame, the genies, Skarmory, Gyarados, Mandibuzz, Gliscor, Latios, Latias, Dragonite, Levitators, and other Flyers, but what other notable OU mon are you hitting super-effectively with Earthquake? Mega-Mawile and Bisharp? Heatran? Aside from those 4, all the other EQ weak Steel types have dropped to UU or lower already (and even some that aren't weak to Earthquake - RIP Bronzong). Poison-types? All the relevant Poison types in OU are either neutral or immune to Ground. Rock-types? Terrakion and Tyranitar are the only relevant ones. Also EdgeQuake coverage isn't that great in OU not only because Stone Miss is such a heartbreaker move. It just doesn't seem worth it running EQ unless you have STAB on it, or it covers up a deficiency in your STAB.
Fire - Yes, there are a lot of good Fire-types in OU right now, which is why Fire attacks are common. But this, arguably, is even more clearly Aegislash's fault. Fire is NOT a good attacking type in a vacuum - it's resisted by the common Water, Fire, and Dragon types. It's SE only against ONE OU relevant type - Steel. However it's rise as coverage for Steel type mons (and the drop in usage of Fighting coverage) is almost 100% Aegislash's fault. This is a problem, guys.
Dark - And now one type where it may seem it's not Aegislash's fault, but it totally is. Dark got a lot of buffs in Gen VI - the nerf to Steel's resists, the Knock-off buff - however Dark doesn't hit anything outside of Ghosts and Psychics SE, and of the 3 Psychics in OU, two are neutral to it. However Dark types are so low-risk to use because you're highly unlikely to be punished with a Fighting-type switch-in or priority, because Aegislash makes running Fighting type mons AND moves too risky.
So, yeah, at least 3 of the 4 "common weaknesses" are in my opinion only common BECAUSE of Aegislash.