Fromm had published almost nothing since 1935 while Adorno surpassed him

Evidence

The Institute had thus parted with a member of staff who had for a considerable time been the most significant one for its theoretical work. After 1935, however, only one article by him had been published in the ZfS. An `essay on principles’, written in 1937, which Fromm wanted to revise on the basis of criticisms by Horkheimer which he had agreed were reasonable, was not published, or at least did not appear in the ZfS. Fromm’s study on the working class never reached a stage at which Horkheimer considered it ready for publication. He was often either ill or taking a cure. He seemed to be closer to circles of psychoanalysts and sociologists that would have nothing to do with an antagonistic social theory than he was to the Horkheimer circle. From the moment Adorno arrived in New York, Fromm had heavily criticized precisely those areas in which, in Horkheimer’s eyes, he was more and more clearly being surpassed in theoretical productiveness during the second half of the 1930s. — Rolf Wiggershaus, The Frankfurt School, 1123