Magic is supposed to be easy, what makes it possible is mana. Special particles that fill the world, or a parallel world connected to it. They are optimized for working with one's consciousness, your consciousness just perceives them as a part of your nervous system. Interacting with mana is as easy as moving one's hand. But, even if it's easy, just like the ability to move things with your hands doesn't open a clear part to godhood, the ability to move things with a new invisible hand changes nothing in this regard.
A different way to do magic is to add a new organ connected to one's brain. A core. Then, your consciousness doesn't even need to interact with mana; it just gives some commands to your core through your nervous system. The core can contain a spirit that does the work for you. Or it can emit some radiation that affects mana particles in the environment. Regardless, cultivating your core is no easier than cultivating your heart, unless it comes with a built-in function for this; but such a function isn't strictly necessary and definitely doesn't need to be limitless.
Cultivation, on the other hand, is supposed to be hard; what makes it possible is countless lifetimes spent refining and purifying one's spirit. Most people can't cultivate; every cultivator is a heavenly genius, one in a billion. Even if their world has / is made of ownerless Qi, which can be used to strengthen one's spirit, an average mortal incapable of perceiving or controlling their own Qi won't be able to touch this new thing as well. So it changes nothing.
Qi is like energy a part of your spirit turns into whenever your consciousness has some intentions. This makes you experience some stress until it finishes the job and returns. When you intend to move your hand, some energy goes into your nervous system, does the job and returns. When you want to lift a stone - this energy makes you use your hand. And if you insist on doing it without a hand, the energy simply keeps growing until you experience pain, but still refuses to leave the brain. Unless you're a heavenly genius.
In our world, the magical part of cultivation is supposed to start with fully mastering a state most people can't experience even once; some people fail even after spending 1000s hours on meditation. And the number of people who have managed to demonstrate some magical abilities before a team of scientists is, like, less than 100, and their abilities are at the level of slowly moving something light a little or setting a piece of paper on fire. This means that even if you have no reason to deny their existence, becoming the best master in our world only grants you the ability to perform circus tricks.
