Six months in the writing, his report is a powerful response to his critics' mistrust with his earlier research. 建议改为：

After six months of writing, his report is a powerful response to his critics' mistrust of his earlier research.

【翻译】经过六个月的写作，他的这份报告针对他的批评者对他早期研究的不信任，是一个强有力的回应。

【简析】Six months in the writing 这个名词性短语，无论语法还是语义，都不清晰。改为：After six months of writing。

“对某事的不信任”，应为：mistrust of something