You could make the case that MegaKangaskhan is one of (if not the best pokemon) in Pokebank OU and deserves to be banned. I am going to elaborate on what I believe to be the grossly under-represented side: that it should be OU.
It absolutely disgusts me how many people think Kangaskhanite should be banned for the wrong reasons. Not having counters/having counters has got nothing to do with warranting a ban. Demolishing walls after you let it set up does not warrant a ban. Incentivising you to run something you didn't used to run (Rocky Helmet instead of Leftovers) does not warrant a ban. MegaKangaskhan doesn't always know what you're going to swap in (or stay in) and can't always predict the right move to use, it doesn't spam Return and hit everything Super Effective. It also has 4MSS but even if it had 8 moves the point is that sometimes it tries to Scrappy PuP (predicting your ghost switch-in) and instead you just stayed in and attacked it, killing it or at least chunking it hard enough that you can now revenge kill it. Sometimes it tries to Crunch the incoming ghost and instead you brought in Terrakion. The reality is that 99% of the people on the pro-ban side have no idea why this thing deserves a ban, and frankly don't know how to play pokemon.
The main reason I think that Kangaskhanite should be left OU is that none of my teams ever run something niche to beat it. MegaKangaskhan is one of the many large threats in Pokebank OU and I don't have more trouble with it than the others. I honestly have more trouble with niche things like Tornadus-T, Deoxys', Rotom-W, etc because these are pokemon you either need something very specific to stop, or pokemon that you can't 'stop' doing what they do because they're just great at their jobs. Meanwhile the tools you use to beat MegaKangaskhan teams are the same tools that are simply good in general. Pokemon like Ferrothorn/Garchomp with RockyHelmet/IronBarbs/RoughSkin are just great pokemon in this metagame. Ghosts with Substitute/WoW are just great pokemon in this metagame. Revenge killers with Extremespeed/other fast priority/scarfers like Genesect are just great pokemon in this metagame. There are plenty of other pokemon that can run away with the game if you give them a turn to set up, or you didn't keep your best checks healthy enough, or you made one bad decision. With team preview there is no excuse to not know which pokemon you need to keep healthy, or how dumb it is to lock into a choiced move early, or any similar setup fodder.
I just don't see how being the best pokemon, or having the best risk/reward, or whatever means that it is suddenly ban worthy. I am under the impression that we only ban things that truly break the game, rendering it unplayable as it was intended to be unless we all run said pokemon. Mewtwo is the classic case of this, you bring Mewtwo on your RBY team or you lose to any good player with Mewtwo on their team. Anyone who thinks MegaKangaskhan is that level of mandatory is crazy as you can witness people above 1850 constantly winning games without MegaKang against teams with MegaKang.
I think DPP Gyarados is incredibly similar to MegaKangaskhan. The Waterfall/Return/Taunt/DD set could always find a way to come in and get off a DD or two, and then run away with the game. It was too strong, too bulky, too fast, had a bunch of viable items, and it's typing was too good. This was DPP, there was no Ferrothorn, the best checks were things like Skarmory with Whirlwind and Taunt turned them all into setup fodder. Nothing could consistently stop him and if he somehow didn't get to set up you still had to fear StoneEdge/IceFang/Bounce coming out of left field to blow by your supposed answer. He was easily one of if not the best pokemon in DPP and played soooo similarly to how MegaKangaskhan plays today that I honestly find the MegaKang tears hilarious.
TLDR: Kangaskhanite should be OU because the tools you use to beat it are the same tools you run to beat everything else. To me banning Kangaskhanite is akin to banning Gyarados in DPP. Yes, its a fearsome sweeper that often runs away with the game, but ban-worthy? Please.