A lot of discussion on the suspect forum isn't necessarly about aegislash and KS, it's about what's the point of banning KS when it's not broken on smeargle (unlike swagger and OHKO moves) and that blanket banning KS while unbanning aegislash at the same time sets a poor example of common tiering procedures used in the test.. they're worried that next thing smogon will go for is banning things like protean greninja and speed boost blaziken just to nerf them enough for OU.
To be honest, I think smogon really needs to get out of the gutter and switch up their tiering methods and arguments. They can never create a balanced metagame no matter what they remove and introduce.. there will always be one mon who tops them all and forces the metagame to revolve around it.
In aegislash's case, I don't see the overcentralization.. back in x/y one can argue that aegislash hurt the viability of pinsir, heracross, gardevoir, and medicham. We look now at the oras meta.. and guess what? Pinsir is RU by usage, medicham and heracross are UU by usage, and gardevoir hasn't really seen much of a change since mega scizor is on the rise without aegislash. Even in pinsir's case, pinsir was S-rank OU during the x/y aegislash metagame! and since.. now sits in the lower tiers with the pinsirite being banned in all but OU. Even gallade, who suposedly is the new medicham, is getting UU discussion as his usage statistics might be dropping him down!
Aegislash shadow sneaks his way back in the meta without much impact.. those everybody claim are unusable by his presence, are overselling those particular pokemon when they cannot properly function in the metagame even without aegislash around. If change wasn't made, than I don't believe aegislash's reintroduction is an issue in the slightest.
The only argument one can use for his ban is the no counter argument.. but look at keldeo, landorus, stall breaker and natural gift talonflame, and metagross.. all four if removed from the tier would make just as much of an impact as aegislash did lifting pressure from teambuilding. They hinder teambuilding just as much with their multitude of sets they can run while forcing teams to overprepare for them and have checks. No counter =/= ban worthy in this case.