Not for nuthin', but this kinda sucks.  I'm sorry but there are STILL gaps, and performance issues that make doing some things easier in the Classic Report Builder, and until all of them are addressed this does nothing except make our job even harder.  

Release Notes

Stay in Lightning Experience When Working with Reports 

• The Reports tab no longer has the New Report (Salesforce Classic) button.
• The Edit in Classic option has been removed.
• The Get Feedback button has been removed from the Lightning Report Builder. The button was used to collect feedback on gaps between the Lightning and Classic report builders.