Salesforce Sales Cloud is the system of record for the sales process because it contains information about opportunities and opportunity products, which are used for forecasting and reporting. It also integrates with other clouds such as B2B Commerce and CPQ to support the cart-to-quote process.

https://help.salesforce.com/s/articleView?id=icx_b2c_crosscloudengagement_systems_of_record.htm &language=en_US&type=5

In the described sales process, Salesforce Sales Cloud serves as the system of record. This is because the overall pipeline, including opportunities and opportunity products, which are central to forecasting and sales management, is managed within Sales Cloud. While CPQ and B2B Commerce play crucial roles in quoting and online purchasing respectively, and the ERP system houses product and primary pricing information, it is Sales Cloud that integrates these elements to provide a comprehensive view of the sales pipeline and performance. This alignment with sales processes makes Sales Cloud the authoritative source for sales-related data and activities, aligning with Salesforce's best practices for sales management and forecasting.