I am truely thankful that we are finally doing this retest.
Now to actually give reasoning why aegislash should be brought back into the tier.. for starters, why was aegislash banned?
Forcing 50/50 situations
Overcentralization, being a blanket check to the entire tier
Having no true counters or hard checks that could reliably switch in
I'm going to narrow down exactly whether or not any of these describe aegislash specifically, cause there is ALOT of bias with these claims from both sides, anti-ban and pro-ban alike.
For Starters, what is a 50/50 situation? Basicly, it's a coinflip.. you either choose move a, or move b, if you choose the wrong one, the opposing player gets an advantage and can cost you the game. If the correct move is chosen, the opposing player could suffer extreme consequences. Does aegislash cause 50/50s? No, infact the 50/50 argument is very stretched for and overdramatized. The move king's shield halves your attack if you use a contact move on it.. however the only time the player is using a contact move is when they're spamming knock off (which the most viable user with it OHKO's and has defiant to ignore the drop), or they're going for a move like waterfall/aqua jet from azumarill (who shouldn't stay in regardless)... other times it's flare blitz or the like from zard or something, which aegislash is never to be up against 1v1 anyway. These 50/50s are incredible rare since most pokemon will only be spamming hard hitting EQs, and special attacks on aegislash for the most part. 50/50s are also in the metagame whether we like it or not.. we have 50/50s everytime we do double switches, even the move sucker punch has just as much mindgame playing and prediction as king's shield.. both only work if you attack, both give setup and status oppertunties, and both put pressure on the player forcing them to choose between move a, move b, switch, or stay in. Likewise, pursuit can see a similar function, stay in and attack, switch out and risk pursuit.. or on the user's side.. go for another attack thinking they won't switch, or predict the switch and actually pursuit.
This "50/50s" are present in the metagame all the time. Aegislash is just a lesser evil of the 50/50 situations, however, I do not believe it is frequent enough to justify him staying out of the tier. Especially when it's more skill based and the player actually has to predict, rather than RNG skillhax like serene grace or flinching that is in neither player's control (looking at jirachi and togekiss).
Is Aegislash overcentralizing? This is a difficult one to answer.. actually the metagame hasn't changed, THAT much since his ban. Gardevoir is still mediocre, M-medicham went to BL without him anyway, same with heracross.. the three pokemon we wanted to remove aegislash for so they can shine. Gallade is the biggest reason medicham dropped.. but even he is starting to see his days now that the hype died down. So the question is, what exactly would lose viability, that didn't already? The only pokemon worthy of this argument is altaria, metagross, diancie, and starmie since everything else is mediocre to begin with or benefit from aegislash's synergy on the team. Aegislash cannot switch into analytic starmie anyway, not to mention scald makes aegislash a very shakey choice to spinblock starmie. I do feel the star would still be alright in the metagame. Metagross and altaria certainly will have a huge issue with aegislash, but to be fair, when something is reintroduced into the tier, it's only what you can expect.. one or more things to be checked or countered by the new addition. Diancie is a bit of a shakey one.. aegislash can't switch into earthpower, and diancie checks the stall aegislash set if it lacks flash cannon.. which it then has mediocre coverage.
One thing people wanted when they banned aegislash, was versatility in the tier... but tbh, higher on the ladder, teams are just lando+keldeo+metagross anyway.. I hardly see any versatility unless they're gimmicks. HO teams look very similar, stall teams look similar, and balance teams pretty much use the same pokemon but try them out in a different way. Even with the introduction of aegislash, lando will still be dominate, and keldeo will still rip teams apart... only metagross will be hurt by his presence.
Does Aegislash have counters? Hippowdon. That's honestly the only one. However with the power creep being such an issue, I don't think checking or RKing aegislash is that difficult.. the majority of the time he is taking chip damage, and with garchomp, lando(t+I), keldeo, sableye, list goes on, being so commonly seen on teams, I doubt aegislash will have many opportunities to cause teams problems. Switching aegislash into anything is going to still force him to take chip damage without recovery. To say the least, it's fairly underwhelming against this gen's power creep. Ghost/steel seems like good typing, but fire, dark, ghost, and ground are some of the most common offensive typings used in OU right now, that his bulk becomes mediocre.
I think the question we ask ourselves is, how much the metagame really change from the first aegislash one? I know a lot of people here will vote ban just because they do not want to shake up the tier again in it's current state, but realistically, it's time we do so as this current meta is staler than any over centralized one I've experienced so far. It's our choice, do we want to keep things the way they are, or do we want to actually shake up a metagame we've being playing the same state? Is aegislash's overcentralization, if there is one, any more stale then what we're experiencing with lando, metagross, keldeo, and sableye right now?
Personally, I think he should be unbanned.