Pro license question

The ability for Pro Users to make changes depend on the context of where the report sits and what access is provided.  In a standard environment, you would have Workspaces created for set groups and purposes.  In those workspaces you can set up who can edit and who can only read the content.  "Publishing" a workspace as an app is the most ideal way of providing access to reports to the business without giving away editting rights.

When it comes to personal workspaces, people always have access to edit their own items.

When a project is being published to the service, you will be shown a Workspace selection, whereby you need to select which workspace you wish to publish to.

To touch on your pro-license question. You are correct, it is not econmical to look at Premium until you reach at least 500 employees that require Power BI access.