While it is true the Vocaloid boom came out of Japan, some of what fans believe is simply a misunderstanding.
Some of the early Japanese producers were in fact either music students or already full/part time producers of music, and some programmers and cartoonists who were also professionals or wannabes collaborated with them. The English fandom originally only paid attention to the Japanese PVs (Music Videos) because of their anime-like nature and much of the Vocaloid fandom in the West consists of people drawn in because of attachment to the characters, not exactly musical interest. However Western Vocaloid fans are beginning to catch up, it is now possible for a Western fan to compete with the Japanese fans. On some occasions, a Western producer has even managed to make it to the weekly Vocaloid ratings, although due to language barriers it is hard for Western fans to get noticed by Japanese fans.
On top of this, due to the favoritism of the Japanese Vocaloids, many western fans attempt to use Japanese Vocaloids without being able to over come the language barrier that is passable by using a English capable Vocaloid. This is a large part of why covers are so common among western composers (such as sango312 and Circus-P), which often makes them seem inferior because they have trouble stacking up to the original.
Also, many elite communities exist within the Japanese fandom that make it easier to create works excelling in multiple aspects. Since some of them are usually by invitation-only and most of the pages are written in Japanese, It is not easy for western users who cannot speak Japanese to join these communities. On these kinds of sites it is relatively simple to find a skilled illustrator for the creation of a PV, and they have an easier time exchanging media-based information. The comment that English fans should not even try to compete is also usually spoken by a Vocaloid listener, not a vocaloid user; those listening to the Vocaloids will rarely share the same knowledge as one using the program.
The overall quality of Western producers' work appears to be much higher. However, since the western fandom is still catching up, many are still working on low budget and low scale pieces and even the bigger users admit a lack of confidence or resources needed to write original works of their own.