Forster can’t seem to read Hamann straight for attachment to Herder. Wilfully misreads him, in fact, and employs tendentious and unexpressed canons of philosophical justification to do so.
Actually, Forster appears to misread Hamann more or less exactly as Herder himself had. In that light it is not that Herder overlooked an injustice done him by Hamann, but that Forster lacks the ‘deferential and generous tendency’ that would acknowledge his own error.