"Weaken" does *not* mean the same thing as "disprove". That's crucially important in GMAT CR. Here we need an answer which suggests that the conclusion might not be true. We do *not* need an answer which *proves* the conclusion is false.

A is not correct, since it's talking about a different band altogether.

B is not correct, since we care about revenues, not about profits, so we don't care if Band 1's concerts were expensive to produce.

C is correct. The argument bases its claim only on album sales and concert revenues. If other bands generated revenue in other ways (films and DVDs), it is possible that those bands earned enough from those other revenue streams to surpass Band 1. Note that the films and DVDs are described as 'extremely lucrative', which suggests they are important revenue sources.

D is not correct, since critical opinion has next to nothing to do with revenue (in real life they might be inversely correlated much of the time).

E is irrelevant since depressed album sales will have affected all bands.