Absolutely fair point which you are making!
I usually tell my case interview coaching candidates (a bit jokingly though) that McKinsey is actually one of the most easiest firms on this planet to get in.
Why do I say this? To make fun of my coaching candidates? No, for sure not - I say this because I want to let them know one of the key issues on consulting interview prep, and it probably holds true in many many other occasions:
It's not always the smartest, brightest, best people landing offers at McKinsey.
It is actually those candidates who know how to prepare correctly.
Or in other words: mastering the McKinsey interview process is more a matter of diligent preparation, than being a genius (for sure you will need good business acumen and a logical way of thinking [a.k.a. being client friendly] - but this is far away from being a genius).
I specifically say that McKinsey is one of the most easiest firms to get in because there is hardly any other firm where you know in that much detail what exactly will happen in the recruiting process (as opposed to many other firms outside the consulting industry). There is no magic in solving case interviews and preparing for the McKinsey PEI (Personal Experience Interview) in a surefire way - it is mainly hard, highly disciplined work and lots, lots, lots of practice. (Or as someone else used to say: it is 10% inspiration and 90% transpiration, and not the other way round!)
Therefore, you have the opportunity to prepare for your McKinsey interviews accordingly - it is up to you to use it, but at least you have the opportunity. There really is more than enough prep material available to do all this, starting from basic knowledge like Victor Cheng, more focused material like my own for the McKinsey PEI as well as interview practice partners here at PrepLounge.
Most definitely McKinsey is a highly regarded brand not only from the client's perspective, but also on the job market. Therefore lot's of strong candidates apply at McKinsey, and they can choose quite freely amoung a very large pool of strong candidates, which makes the whole recruiting process really competitive (in conjunction with the general recruiting mindset that they rather like to err on false negatives than false positives) - but given all the opportunities for in-depth interview prep, I can't except a lot of excuses for not getting at least extremely close to getting an offer from McKinsey (yes, as with everything in life, there is no 100% guarantee whatever you will do in your prep).