Ok, several reading comprehension issues there.
And I specifically stated why CB doesn't outperform it... like I said, it's Choice band. So many things in OU have a greater effective stat than mega medicham thanks to CB. That doesn't necessarily make them better...
Actually no. Virtually nothing is stronger than Megacham's HJK in OU even with Choice Band
except Mienshao and a few weather boosted attacks. That's the whole allure of Megacham in the first place, so Mienshao's outpowering it is no small feat.
252 Atk Pure Power Mega Medicham High Jump Kick vs. 0 HP / 0 Def Arceus-Electric: 303-357 (79.5 - 93.7%) -- guaranteed 2HKO
252 Atk Choice Band Reckless Mienshao High Jump Kick vs. 0 HP / 0 Def Arceus-Electric: 318-375 (83.4 - 98.4%) -- guaranteed 2HKO
252 Atk Choice Band Teravolt Kyurem-B Outrage vs. 0 HP / 0 Def Arceus-Electric: 307-363 (80.5 - 95.2%) -- guaranteed 2HKO
252+ Atk Choice Band Adaptability Crawdaunt Crabhammer vs. 0 HP / 0 Def Arceus-Electric: 290-342 (76.1 - 89.7%) -- guaranteed 2HKO
252 SpA Solar Power Mega Houndoom Fire Blast vs. 0 HP / 0 SpD Arceus-Electric in Sun: 366-432 (96 - 113.3%) -- 75% chance to OHKO
And megacham doesn't need U-Turn when substitute is standard on it. It can stay in on latias/thundurus and possibly KO it while it tries to break sub... which is just as good, isn't it?
I never stated U-Turn was a necessity, but it's clearly an advantage that Mienshao has. Why? Because two defensive types that you'd switch into a Fighting move, U-Turn is SE against for one. Second, you get to pick your matchup. You know how easy it is to Pursuit trap Gengar, Latias, Mew etc. when you U-Turn to Bisharp or Tyranitar?
252 Atk Pure Power Mega Medicham High Jump Kick vs. 252 HP / 0 Def Mew: 194-228 (48 - 56.4%) -- 32% chance to 2HKO after Leftovers recovery
Apparently the usage spread for mew is Will-o-Wisp, knock off, a recovery move and a filler, with 0 defense EVs (according to the calculator). Will o Wisp won't get to medicham because of substitute, and... dude. You can 2HKO a pokemon with 100/100 defenses with a resisted move because lol.
Again, Mienshao's HJK is even stronger, so showing damage calcs for Megacham's HJK is moot. Also...
252 Atk Choice Band Mienshao Knock Off (97.5 BP) vs. 252 HP / 0 Def Mew: 308-364 (76.2 - 90%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Choice Band Mienshao U-turn vs. 252 HP / 0 Def Mew: 224-264 (55.4 - 65.3%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Choice Band Mienshao Knock Off (97.5 BP) vs. 252 HP / 252+ Def Mew: 222-262 (54.9 - 64.8%) -- guaranteed 2HKO after Leftovers recovery
252 Atk Choice Band Mienshao Knock Off vs. 252 HP / 252+ Def Mew: 150-178 (37.1 - 44%) -- guaranteed 3HKO
Mienshao can always 2HKO standard stall breaker Mew with Knock Off and even has a very good chance of 2HKOing max/max Mew with Stealth Rock down. You could also just as well U-Turn, get Mew below 50% and get a good set up sweeper in place.
Lastly, Note that MegaVoir can only run one set at a time lol, so it can't wallbreak and cripple stall at the same time. Chansey can hold it's own against megavoir, getting 3HKO'd by psyshock which is okay, then again it's CHANSEY. Apart from that it rips apart standard specially defensive walls
Mega heracross being able to defeat medicham 1v1 doesn't matter much. And anyway...
252 Atk Pure Power Mega Medicham Zen Headbutt vs. 40 HP / 0 Def Mega Heracross: 390-458 (125.4 - 147.2%) -- guaranteed OHKO
A simple combination of Hyper Voice and Taunt is all Gardevoir needs to walk all over a majority of Stall pokemon, with a the addition of Psyshock, Substitute, Calm Mind, Focus Blast and Wish do do numerous other things.
And I never said anything about Heracross and Medicham going 1v1, that's irrelevant. Heracross is better for having far better bulk, Swords Dance, and his Skill Link attacks being able to break through Subs, Focus Sash and Sturdy users.
Again, virtually all the praise you've given to Medicham is outperformed by something else. Describe what's uniquely good about him.