Option(D) is correct
There are two major problems with this sentence.
(1) The subject (his writings, which is plural) does not agree with the verb (is, which is singular). Since the words his writings are located outside the underlined portion, the verbis must be changed to are.
(2) The idiom more often than is intended to compare the writings of Douglas Kysar with the writings of other young legal scholars. However, the original sentence compares Kysar's writings with other young legal scholars. It does not make sense to compare writings to people. The correct comparison should compare the writings of Kysar to those of most other young legal scholars, where the pronoun those clearly refers to legal writings--not young professors.
A. The subject (his writings, which is plural) does not agree with the verb (is, which is singular); the writings of Douglas Kysar are illogically compared to other young legal scholars
B. The writings of Douglas Kysar are illogically compared to other young legal scholars
C. The subject (his writings, which is plural) does not agree with the verb (is, which is singular)
D. The subject (his writings, which is plural) correctly agrees with the verb (are, which is plural); the writings of Douglas Kysar are correctly compared to those [referring to writings] of most other young legal scholars
E. The writings of Douglas Kysar are illogically compared to other young legal scholars; the are is awkward