Are all the pen copybooks sold in bookstores written by calligraphers themselves? Can anyone really write to this extent?

Of course, and it should be written by the calligrapher himself. This level is not very high, and usually calligraphers with certain attainments can easily reach this level. But usually calligraphers' writing tools are very different from those we usually use, which is why a clever woman can't cook without rice. There is no way. They are professionals and we are amateurs.