If someone's copied calligraphy works are very similar to the original, they can be confused with the real. Just proving that his imitation ability is very strong does not mean that his artistic level is very high. The main criterion for evaluating the artistic level depends on the person's creative level.
When we look at ancient calligraphers, although we say that we must be close to the post, we say that "the viewer is still refined, but the painter is expensive". Many ancient masters are not very similar to the ancient works they copied. For example, Zhao Mengfu copied Wang Xizhi's Preface to the Holy Teaching. Do you think so? Anyway, I don't think it's very similar, but he can be called a master, because his creative ability is very strong, and even the copied works have their own feelings.
There are also some calligraphers, such as Wang Duo, Mi Fei and so on. Wang Xizhi's calligraphy near them has its own flavor. They don't just imitate it.
Nowadays, many students majoring in calligraphy have very strong imitation ability. Many students in the Academy of Fine Arts can even imitate the works of ancient masters one-on-one, or even confuse the fake with the real, but the creation is seriously out of touch with the copybook, but they can't write their own works.
Copying is a kind of ability, and creation is another kind of ability. The most important thing is to internalize the knowledge learned from copying into your own knowledge. This is clever plagiarism, not plagiarism for plagiarism's sake. Why are the ancient masters so different? There is a simple reason. They wrote their own understanding of copybooks, not pure imitation. If you want to learn calligraphy freely, you must get out of this strange circle of pure imitation, or you will never create it.
Of course, it is undeniable that some people can not only look alike, but also create excellent works of art.