I don't fully agree with that about the legato lines, though it is true you hear the uniformity of sounds with legato when there are repeated legato phrases - that is a huge problem, almost like the machine gun effect. The Legato Machine Gun Effect. In other words, if you have an ostinato that keeps repeating a legato skip from a middle C to an A above it in eighth notes, it will sound artificial in almost the same way as a single note sample being used on a repetition. This is such a problem because it is, at least with this technology, not correctable without sampling alternate legatos. Which is a huge undertaking. A single legato instrument is a huge undertaking! So perhaps in the future VSL will be able to develop an engine that creates alternations in legato transitions via scripting.
However what I don't agree with is on a less repetitive legato line, you don't really hear that extreme uniformity of sound all that much. It can sound quite natural when exposed. Witness the other Bacal work on the Vaughn Williams Fantasia.
That is an interesting point about the difference between playing a pre-existing work and one's own new work. It brings up the questions of how much a composer is influenced by the sounds available right in front of him, how difficult it is to use them, how lazy or compromising he is in doing the performance. Right now I am looking on the VSL as a huge reservoir of sound, a vast ocean of possible expressions, into which one can dive and swim for months (like Jay) or which one can dip one's toes in. But it allows you to do either stiff, poor performances or beautiful expressive ones, based on how willing you are to use its full potential. As has been said before, this is the same as a great musical instrument that one can play badly or brilliantly on, based on musical ability.