I don't really see how Aegislash would be any easier to deal with now than it was in XY. In fact, one could argue that it's become even more effective because it dumps on a bunch of the new Megas (Altaria, Metagross, Sableye depending on the variant, Diancie, Slowbro, and unboosted Gallade -- and Lopunny has to win a 50/50 and Beedrill has to predict correctly yet is still checked). All of its devastating old sets, those being the standard tank, SubToxic, LO attacker, and fast SD, are just as if not even more effective due to the enormous decline of Mandibuzz and SpD Hippowdon. It's still completely uncounterable (SpD Gliscor comes close but with a 4x weakness to Ice and Aegislash's gargantuan Special Attack it's not hard to see what people might come up with). Moreover, Aegislash completely destroys the metagame as it stands. Aegislash singlehandedly makes pretty much all of the defensive Psychics, such as Jirachi, Celebi, Starmie, Mew, and Cresselia, unviable just by its presence in the metagame; if you don't believe me, look at usage stats from last spring/summer as well as the usage stats from the last WCOP and SPL (the one before this one). Seemingly simple differences like Metagross running Earthquake over Hammer Arm and Azumarill running Knock Off reshape how the metagame handles these Pokemon. For instance, Mega Metagross without Hammer Arm is walled by Ferrothorn and Mega Gyarados. Ferrothorn no longer has to play mindgames switching into Azumarill because the threat of Superpower is gone and AV Azumarill rises in popularity due to its ability to check Aegislash, which makes it easier to handle defensively. I suppose you could say that Aegislash helps keep some things in check, but that is not and never has been a reason to unban a Pokemon as we don't use broken to check broken, instead we ban all of the broken elements.
Genesect is another story entirely because I have actually talked to some good players who don't think it's broken, but I still don't think it's really justifiable. There's this unhealthy overcentralization that anyone who played either XY with Genesect or BW with Genesect knows well. Barely anything can handle standard Genesect sets (the main ones being Band, Scarf, and LO) and that's not even taking into consideration the practically infinite supply of viable Genesect sets. Genesect can pull off virtually any type of offensive set effectively, whether it be pure special, specially based mixed, physically based mixed, Band, physically based Scarf, specially based Scarf, EBelt, Shift Gear, Specs... it's just insane. The Pokemon that's hailed as the primary Genesect counter, Heatran, is so easy to take advantage of with hazards + U-turn and partners that can pressure it (there's so many of these, lol). Even when you get manage to bring something into Genesect, it maintains momentum with U-turn and thus you're pretty much screwed either way. There's such a lack of viable counterplay to Genesect that I can't really see how it's healthy for the tier.
In this metagame, there's two things that a lot of others have commented on and that I certainly believe should be dealt with immediately, those being Mega Metagross and Mega Sableye. I'll only talk about Mega Metagross in this post just because this post specifically is already long. Mega Metagross defines the current state of offense and balance by being so ridiculously threatening and effective. Metagross has it all: an excellent Speed tier, crazy bulk, and insane offensive capabilities. In one Pokemon, these traits make it almost impossible for offense to deal with effectively. While there are some methods of counterplay, mostly revolved around revenge killing, Mega Metagross can set up an Agility to sweep the entire offensive team or even just put enormous pressure throughout the entire game. Offense has to spend the entire game dancing around Mega Metagross because it's so hard to put legitimate pressure on and can take advantage of so many common Pokemon. Balance is sorely lacking in defensive answers as well, especially when it's taken into consideration that Grass Knot invalidates the likes of Slowbro (to an extent) and Hippowdon as defensive answers. Physically defensive Gliscor and physically defensive Mew can serve as ok-decent counters, but lose the moment they incur any type of prior damage that they can't manage to heal off, and lose 20% of the time regardless due to Meteor Mash's capability of boosting attack. Gliscor is slaughtered by the occasional Ice Punch as well and usually prefers to run a specially defensive set, but can be forced to go physically defensive just to handle Metagross. There's a couple other things, but pretty much all of them are temperamental and prone to being worn down or eliminated by the right coverage move. The sheer amount of devastation that Metagross causes combined with its excellent bulk is more than enough to ban it.