1. Salesforce Help, "Account Teams": "An account team is a team of users who work together on an account... You can specify each team member’s role... and level of access to the account and its contacts, opportunities, and cases." This document confirms that Account Teams are the single feature designed to manage access to an account and its related standard objects.
2. Salesforce Help, "Set Up Account Teams": Under the section for setting up teams, the documentation details the ability to define team member access levels for Account, Contact, Opportunity, and Case. The available access levels for Opportunities and Cases are "Private," "Read-Only," or "Read/Write," directly enabling the solution described.
3. Salesforce Architects, "Record-Level Sharing: Under the Hood" (White Paper): This document explains various sharing mechanisms. It positions teams (Account, Opportunity) as a method for flexible, user-managed sharing on a record-by-record basis, contrasting them with the automated, criteria-based nature of Sharing Rules. This supports why Account Teams are appropriate and Sharing Rules are not.