The problem is that the existing monitoring platform's notification system is too slow for time-critical issues after migrating to GCP. Stackdriver, being native to GCP, offers faster integration and alerting capabilities. Option C suggests using Stackdriver to capture logs and trigger alerts (leveraging its speed and GCP integration) while shipping logs to the existing platform for other monitoring needs. This approach addresses the notification speed without fully replacing the existing system. Other options like A (full replacement) or B (installing agents without alerting setup) are less targeted, and D (AB testing) doesn't resolve the core issue.