His academic papers often are viewed as being ponderous.

The word 'ponderous' means slow and clumsy because of great weight; in the context of writing, it means dull, laborious, or excessively solemn and difficult to read. Profound (deep), difficult (hard to understand), and informative could all describe heavy academic writing. 'Elegant' means graceful and stylish, which contradicts the heavy, dull connotation of ponderous. Therefore, elegant is the odd one out.