That is on its face defeatist. I can name several people I know personally that have learned English to that of a native speaker, and far beyond their native language. (In fact, their native languages have atrophied considerably most of the time.)
I do not like discussing language acquisition as a skill, because it often ignores the social and cultural components of how we communicate, and the general knowledge that any native speaker will have. However, language is absolutely a skill that is learned the way we learn everything else. To acquire skills we need:
- Many attempts with feedback
- Timely feedback
- Deliberate practice
When you think about kids babbling, they get feedback constantly on whether they are following the implicit rules and being understood. (I probably set back my friends’ children years in their language development when I pronounce the “th” sound “d” like they do.)
In chess, you will fall for the same trap a thousand times until you remember it. In language, you will use the wrong preposition or case a million times until you remember it. The key is - is someone telling you it is “wrong”.
On timely feedback, being mad at my dog because she pooped in the house is not helpful when that feedback is given hours later. The feedback needs to be tied directly to the action, or all you have is a dog that has no idea why you are upset. This is why it can be helpful to do Anki or SRS after reading something, or answer questions like a test.
Deliberate practice is something I think you misunderstand. Deliberate practice is when you are putting yourself slightly outside your comfort zone. Learning requires you to be constantly inching up the difficulty into a growth zone. With language there are so many interlocking mechanisms that need practice. You are taking oscillating pressure waves that vibrate little bones in holes in the side of your head, which collide with little nerve endings deep in those holes that convert the mechanical action into electrical impulses. Your brain then interprets those electrical impulses into meaning, decides how to respond, encodes a message and instructs wet air bags in your chest to send air in a precise pattern out different holes in your face while vibrating things on the way and simultaneously moving a large boneless muscle. That is so much stuff, and a deficiency in any area will immediately be noticed by a native speaker. And this doesn’t even touch on reading and writing!
Drilling Anki for 2-4 hours a day is not necessarily deliberate practice, nor is it necessarily effective. You need to break off each one of the requirements and be uncomfortable in short increments for a long time. It takes your brain time to process information and form neural networks. How long? Well, there are two components – duration and time spent in deliberate practice. How much time you get in active study a day without killing yourself will decrease the duration needed, but it is not possible to cram.
Is it possible to “catch up” to a native speaker? Well most native speakers do not deliberately practice their native languages as adults and it is nearly impossible to make them uncomfortable (unless you expose them to Scots). So the answer is almost certainly, look at immigrants that moved and learned the lingua franca. However, the entire premise to this question is ego driven. Why are we comparing ourselves to anyone else? Especially to people in an abstract sense? I personally am only in competition with myself in what I want to get better at. Why do I do anything? Because it is important to me.