Is there a way to get a comprehensive breakdown of cube tables that are used across all dashboards?

Hey newbie12 

There is no native feature. You will need to write a python script that this ór you can import the sisense application database. This contains both the information regarding dashboards and elasticubes. It will take some modelling, however when you get to finish it , it will be a very scalable solution that is very easy to use. 

Another option would be the use Benji_PaldiTeam 's Field Analyze plugin (https://www.paldi.solutions/sisense-plugins/field-analyzer) . This gives you an intuitive UI to get this information

Hamza