Why is inimitable wrong? Carcass

To choose a choice for the first blank, consider what the opening modifier tells us about Susan: she is "experience and proficient (skilled)."

Mediocre (not very good) doesn't work because it conflicts with "proficient."

Amateur doesn't work because it conflicts with "experienced" and "proficient."

Reliable works because a trumpeter who is "experience and proficient" would be reliable.

The word that fills the second blank will fit with the fact Susan's music is more satisfying than Carol's, and it will contract with brilliant.

Inimitable (impossible to imitate) doesn't work because there's no indication that, by being less satisfying that Susan's music, Carol's playing is impossible to imitate. Also, inimitable doesn't contrast with "brilliant." After all, brilliant music would likely be difficult to imitate rather than contrast with being impossible to imitate.

Similarly, influential doesn't work because there's no indication that, by being less satisfying that Susan's music, Carol's playing is influential. Also, influential doesn't contrast with "brilliant." After all, brilliant music would tend to be influential.

Erratic (irregular, unpredictable) works because it explains why Susan's reliable music is more satisfying than Carol's. Also, erratic contrasts with brilliant.

The correct answer is reliable, erratic.