Maca, 

I agree this is a challenge and is difficult OOTB. Last Updated is not helpful in this scenario. You could consider some custom configuration options that may give you the results you are looking for…

First, what are the updates your users make on the Requests that you would want to trigger as an update or “progress” on the request? Understanding this will help you configure a custom solution that will give you data points that you can work with. Examples / Options...

1. create custom fields that capture changes made by any users other than System. You can create fields that will contain what was changed, when it was changed and by whom. This would require a WFR to update the custom fields. You can also create a custom field that shows last updated date (when not system) and even a field named Days or Count or other name that will reflect number of days since last updated by a non-system user. This value can then be used within a report without the need of a custom formula field or the formula field you have can be used against the custom date field instead of Last Updated On. 
2. Another option can be to create an “Audit Log”. This is not complicated. This is simply a Workflow rule that triggers based on changes to specific fields and/or by specific users. The rule would create a Post stating details, for example… Status was changed from Submitted to In Progress on 12/21/2023 by Maca Moran. The posts you create can be different depending on the change made to the request object. 
3. You can create a workflow rule that updates data using the function IsManuallySet(). That may help. 

I hope some of these options help you get your desired results. Happy Holidays!