Accident analysis includes the concept of the chain of events. The fundamental premise being that there's not usually just one mistake that leads to an accident. It usually takes several, and sometimes many mistakes, before an accident finally occurs.
Likewise, it's oversimplistic to say that a game console failed solely because of one factor. The failure of a retail product nearly always involves multiple factors, and the same is true here. So presumably your question isn't literally asking of the distribution issues were the cause of failure, but rather were those issues one of the several factors (besides those you mention and others).
I would say that the answer is definitely yes, distribution played a part in the lack of success of the Sega Saturn. Besides your own reference, which I see no reason to discount, there is the corroborating claim:
Lack of distribution may have contributed significantly to the failure of the Sega Saturn to gain an installed base. Sega had limited distribution for its Saturn launch, which may have slowed the building of its installed base both directly (because consumers had limited access to the product) and indirectly (because distributors that were initially denied product may have been reluctant to promote the product after the limitations were lifted). Nintendo, by contrast, had unlimited distribution for its Nintendo 64 launch, and Sony not only had unlimited distribution, but had extensive experience with negotiating with retailing giants such as Wal-Mart for its consumer electronics products.
From Technological Leapfrogging: Lessons From the U.S. Video Game Console Industry (this is also cited by the Wikipedia Sega Saturn article)
Note that this passage describes not just the relative lack of distribution, which would inherently constrain sales of the console, but also the fact that Sega chose to provide the console only to select few retailers, leading to other retailers not helping to promote the console later when it was more widely available.
More details on that are available in the same Wikipedia article.
Cause and effect are notoriously difficult to prove. Only a robust scientific experiment can really nail down exactly what factors are causal and which are not, and there's no feasible way to perform that experiment. So any claim of what exactly caused the failure of the Saturn is always going to be debatable.
But it seems that there is plenty of evidence to suggest strongly that distribution problems were at least one of the factors that led to failure.