Saying that technical mastery confers automatically artistic qualities to a work would be like saying that physical beauty in a person is what makes a person beautiful.
We all know that a beautiful person has a lot more to offer than her/his physical beauty. But let us not fall in the absurd, it is also clear that the absence of technical mastery will never allow a work to become a work of art on the merit of its content only. We all know that an interesting person does not necessarily render a person beautiful but we all also know that an interesting person that is physically beautiful is undoubtedly a beautiful person.
In other words, an artist has to possess some mastery in his technique in order to express himself with ease. Yes that is the point of a mastered technique, the one who masters a technique can express her or himself with ease.
How could one without technical mastery be able indeed to express her or himself unhindered?