Setting opportunity access on the role to View All opportunities associated with their accounts allows sales users to view all opportunities that are related to accounts they own or are above them in the role hierarchy. This meets the requirement of giving sales users access to opportunities that are tied to accounts they own. Setting organization-wide defaults for opportunities to Private restricts access to opportunities by default, so that only the owner and users above them in the role hierarchy can view them. This meets the requirement of giving sales users access to opportunities they own.

Explanation
When a Salesforce admin assigns User A as the owner of an opportunity related to User B's account, User A will have Read-Write access to the opportunity's Account and its related contact records. This is because of the implicit sharing rules that grant access to parent and child records based on the organization-wide default settings. Since the organization-wide default setting for Account is set to Private, users are unable to see each other's accounts by default. However, when a user owns an opportunity that is related to another user's account, the user gains Read-Write access to that account and its related contacts, regardless of the sharing settings for those objects. This ensures that the user can view and edit the account and contact information that is relevant to their opportunity.

The most likely cause of the records failing is that updates to child records that have the same parent record are being processed simultaneously. This can cause the records to fail because child records must be imported after the parent records have been imported, and if the parent record is being updated at the same time as the child records, the import will fail. The other options are not likely to be the cause of the failedimport.