Quite simply, you're wrong. In the past, when world records weren't so great, sure anyone could achieve it. And certainly in events that have yet to get close to the human limits, perhaps anyone with enough practise could get there.
But every individual person has their own physical limitations. As stated before, practise as much as you like, you will most likely never be able to outsprint Usain Bolt, because his body is physically superior at that ability. Most people have bodies that are literally not physically capable of moving fast enough to keep up with Bolt (even if you took performance enhancers).
The same thing goes for a range of skills. Each individual has their own limits, and those limits aren't the same for everyone. If we assume that Feliks has limits superior to most people, and we assume that he is near those limits, then we can assume he has pushed times down to where most people would be physically incapable of matching him.
It might be hard for you to understand if you are someone who has limits similar to Feliks. You probably think "but it's easy for me, I don't get why anyone else wouldn't be able to if they just tried hard enough". This is a natural reaction, because by me saying "genetics are important" you feel your hard work practising is undervalued.
But let me ask you this: in your life experience, have you been able to run as fast as everyone else? Have you been able to jump as high as everyone else? Have you been able to bench press as much as everyone else? Have you been able to throw a ball as hard and far as everyone else? Do you excel at physics, chemistry, biology, maths, English, fine arts, acting, singing, writing, debating, geology, astronomy, dancing, orating, psychology, and medicine like everyone else?
Everyone has strengths and weaknesses, and not everyone has the ability to be good at everything. Processing speed (look it up) is a thing that people have in different capacities, and to be world class at speedcubing requires a high capacity, that is genetically determined, that not everyone will have.