Darktrace for Email vs. Newer API-Native Platforms

A user is evaluating email security solutions to replace Mimecast, which is considered outdated with too many false positives and vulnerabilities against modern Business Email Compromise (BEC) attacks. Darktrace is being considered for its AI self-learning approach, but mixed reviews mention issues with tuning time and alert fatigue. API-native alternatives (without inline gateway, integrated with M365) are also being studied for their ability to detect BEC and account takeovers without payload, with autonomous response and few false positives. The question focuses on the configuration effort and the quality of detections in production for these solutions.