Graphus is a purpose-built solution to automatically detect and protect against social engineering attacks with a built-in capability to investigate suspicious emails in minutes and facilitate incident response if necessary.
Splunk Enterprise Security with Google Cloud Plug-in is a DIY solution for administrators to collect logs and events for further manual analysis. It doesn't automate the detection of social engineering threats.
From Splunk Website:
The Splunk Add-on for google cloud platform allows a Splunk software administrator to collect google cloud platform events, logs, performance metrics, and billing data using Google Cloud Platform API. After the Splunk platform indexes the events, you can analyze the data using the prebuilt panels included with the add-on. You can then directly analyze the data or use it as a contextual data feed to correlate with other Google Cloud-related data in the Splunk platform.