What is the difference? Or is it grammatically wrong?
all the time
And if you make such a proposal, it will be wrong?
The best artists of the time (When you add the article the list is reduced)
"Of all time" means, essentially, ever. "The best artists of all time" means the best artists of any time, across all time, ever. This gets rephrased as "all time best", or "all-time best", but that means "best of all time"; the rephrasing loses the 'of' as "all time" becomes an adjunct (or attributive) noun phrase.
"All the time" means, literally, "always", or "at every point in time". "You're reading all the time" literally means that the person so addressed is always reading, never not reading. Figuratively it just means they spend an awful lot of the time reading. It is almost never used literally, though - it's used figuratively almost without exception, and when it's used literally people will say something else as well to make that clear.
"The best artists of the time" means, over some identified period of time (say, the 1980s), the best artists at that time. So if you're talking about the 80s, or even, say, 1985, and refer to "the best artists of the time", you mean the best artists of the 80s, or of 1985.