Is In-Depth Understanding or Mastery of Excel Necessary Before Learning Power BI?

Right now, I'm in the process of trying to gain an in-depth understanding of MS Excel, as well as how to use it in various cases - whether trying to collect data, building dashboards, and interpreting data results. Now the question is, should I try mastering Excel first before moving towards Power BI, or is it inconsequential?

Also, how exactly is Power BI needed when MS Excel in itself is capable of housing dashboards and charts?