Does disabling objective goals have any effect?

[joncnunn]

Emphasis added...
You are sending mixed messages here. The numerical modifiers are small -- but they are all small. Adjusting a range by 2 on a scale of 10 seems like it would be reasonable to characterize as “fairly minor” (as in most people would say that “20%” is minor) but in actual gameplay, small changes (in the right place) result in remarkably different AI behavior.

But the biggest effect is removing the threat of AI CV and, accordingly, this allows the player to be much more leisurely about their own VC. From this perspective, every game with CV disabled will have at least one or two AIs that have been crippled.

Perhaps I wasn't clear, AI Brazil is crippled with culture victory disabled because it's behavior doesn't change enough.
They would have needed to code in both a ceiling to the AI "build culture" flavor of 3 and a floor to the AI "build science" flavor of 8 when Cultural Victory is disabled to prevent crippling most cultural AIs, but even then AI Brazil would need to start on the edge of Jungle rather than in than in the middle of it to be competitive.