I think, everyone CAN achieve pretty much everything and can get at good as osu! as they want.
Therefore, I DO believe that EVERY person can, IN THEORY, surpass Cookiezi.
In praxis, that won't happen too soon. Because Cookiezi is the most talented person. Therefore, in order to get to his skill level, he didn't need as many plays, he didn't need as many years of practice as other people would.
The more talented you are, the less you have to practice to achieve a goal. Everyone can stream 250 BPM or higher. But some people will need twice as much plays than others to do so. If you're an untalented person, you need to practice more than a talented one.
Still, if you have enough patience and enough will power (and enough time, since you'll have to spent a lot of it), you can be better than a talented person as an untalented.
voted nurture