He was more popular after he had started singing compared to his writing career, singer/songwriter Barry Manilow still prefers writing to singing.
A) He was more popular after he had started singing compared to his writing career INCORRECTWrong idiom: more x compared to y
Correct idiom: more x than y
comparison error: singing vs writing career
correct comparison: singing vs writing
B) Being more popular after he had started singing as compared to his writing career INCORRECTWrong idiom: more x as compared to y
Correct idiom: more x than y
comparison error: singing vs writing career
correct comparison: singing vs writing
C) Though he is more popular as a singer than as a writerCORRECT
Correct idiom: more x than y
Correct comparison: singer vs writer
D) Although he was more popular after starting to singing when compared to his writing career INCORRECTWrong idiom: more x when compared to y
Correct idiom: more x than y
comparison error: singing vs writing career
correct comparison: singing vs writing
E) He had been more popular after starting to sing than in his writing career INCORRECTCorrect idiom: more x than y
comparison error: singing vs writing career
correct comparison: singing vs writing