I find the kind of thought process that goes behind determining how powerful a Pokemon is currently is outdated. The Megas have completely changed the field of play in that they are all incredible powerhouses and perfectly capable of beating one or two Pokemon all on their own. That's the entire point. Otherwise we might as well ban every single Mega right now because nearly every single one of them are strong enough to warrant banning at some point, including those "lower-tier" threats like Mega-Absol, Mega-Banette, Mega-Aggron, Mega-Venusaur, Mega-Blastoise and so forth. The metagame should be centralising around the use of Megas which I feel should be the defining factor of 6th Gen OU like how 3rd Gen was defined by stall in the form of SkarmBliss with Spikeshuffling and their counters, 4th Gen had this huge hoo-ha about Dragons and Sandstorm, 5th Gen had weather. I think that a metagame where teams move strategically using the Mega as a rallying point for their main strategy should be the equilibrium this generation.
Take for example Mega Aggron which literally no one has considered:
+2 252+ Atk Parental Bond Mega Kangaskhan Return vs. 252 HP / 0 Def Mega Aggron: 126-150 (36.6 - 43.6%) -- guaranteed 3HKO
+2 252+ Atk Parental Bond Mega Kangaskhan Earthquake vs. 252 HP / 0 Def Filter Mega Aggron: 249-294 (72.3 - 85.4%) -- guaranteed 2HKO
+2 252+ Atk Parental Bond Mega Kangaskhan Fire Punch vs. 252 HP / 0 Def Filter Mega Aggron: 189-222 (54.9 - 64.5%) -- guaranteed 2HKO
252+ Atk Mega Aggron Iron Head vs. 0 HP / 0 Def Mega Kangaskhan: 153-180 (43.5 - 51.2%) -- 6.3% chance to 2HKO
252+ Atk Mega Aggron Brick Break vs. 0 HP / 0 Def Mega Kangaskhan: 192-226 (54.7 - 64.3%) -- guaranteed 2HKO
Who can check Mega Kanga without Earthquake fairly well and smash it right back in the face.
tl;dr - Megas are meant to be broken and fight each other
Even comparing against other ban candidates in the past, Mega-Kangaskhan is nowhere as broken as past threats like SubSD YacheChomp at the start of DPPt, who forced you to run three bulky waters/Dragons with a powerful Ice/Dragon move in order to take it down for sure because of Sandstorm and Sand Veil (of which the pool more or less consisted of defensive Starmie, Vaporeon, Cloyster, Salamence, another Garchomp). All Mega-Kangaskhan really asks for is maybe one dedicated counter that can still be used to wall other Physical threats maybe with a Rocky Helmet and one revenge killer who can live a +2 Sucker Punch (who will probably be useful to KO other threats or even sweep on its own lategame). That's it. Mega Kangaskhan can beat entire teams -- Nasty Plot MixApe did that for Gen 4 as well, you had to run a counter for it or instantly lose. "MixApe 6-0s this team, try again" was an incredibly common comment on many RMTs back then, it never came close to a ban. Mega Kangaskhan sweeps you -- Well Mega-Lucario, Mega-Charizard (both of them), DD Mega-Tyranitar all bust huge holes in teams, are you going to ban them too? Mega-Kanga has a lot of reasonable checks, some of which haven't even been discovered. A ton of Pokemon in OU require dedicated checks or are dedicated checks themselves. This isn't really any different from say Dragonite, Terrakion, Lucario, Garchomp or any other set-up sweeper other than the fact that you can't stay in on Power-Up Punch with a low HP Pokemon as opposed to staying in on Swords Dance/Dragon Dance and getting in a free hit.
I ran a mono-Flying team with Masquerain/Crobat/Mega Charizard Y/Togekiss/Gliscor/Talonflame and didn't lose to a single Mega Kangaskhan I ever met, if that means anything.