I still think there are a couple of different elements in play here. I agree that artist testimony matters when it comes to the question of what they're trying to express, or what their inspirations were, or whether they're trying to write a concept album (as well as the question of whether a certain album is "by" a certain band or project, assuming the artist(s) in question are controlling members of that band/project). But I think genre is a bit of a different matter.
If the members of Dream Theater came out and said "Pull Me Under was inspired by disco," and they were really telling the truth about what was in their minds when they wrote the song, then they're right, because that's a statement about intent or inspiration. Same if they said "Pull Me Under was our attempt at disco"—they're the ones who know what they were attempting to do, so their testimony is what we need to know whether that statement is true. But the statement "Pull Me Under is a disco song" is different, to me. Because that's a statement about what the music actually sounds like. And that's one where I maintain that DT could call it a disco song all day long, and even have really meant to make it a disco song, and it still wouldn't be disco because it's just not disco.
To return to this scenario: If Arjen says "This is a Star One album," or "I approached this with the intent of writing a Star One album" or "I was inspired by the sound of the previous Star One albums and wanted to write another like them," then we need to look to his testimony to determine the truth of those statements. If he's accurately reporting the state of his mind, in the latter cases, and his final decision on project titling, in the first case, then those statements are true regardless of what we think about the music itself. But if Arjen says "This album sounds like the other Star One albums," then we need to listen to the albums in question in order to determine whether we agree with him or not, because it's a statement about qualities of the music itself.