There are two people. One speaks a second language and one does not. The one that speaks the language practiced for N years.
On the surface, the other one looks N years behind. It sure can be the case. For example, if N=1, then that person is more or less a year behind.
But he can also be lightyears behind. Because the one who practiced had been to so many places at that point. The people he’d talked to, the things he consumed, and the things that consumed him (!), you can’t measure those things. Those also led to so many different ways, and opened brand new doors. So, he can’t transfer all that to the other one if he wanted to. He can’t lift him up and make him digest things the way he does.
The same thing happens when you argue, conversate or debate somebody. If you haven’t been to all those places, you can’t see everything like him if you tried to. And vice versa. In a way, it is a hopeless case. You’re better off doing something else if it’s not life-or-death.