Best DB approach for a lot of updates
Relational DB seems a perfect fit for your needs. 

MySQL will probably give you some hard time on some of the queries you want to run or you need to off-load that to the application side but that doesn't mean it cannot be done. Depends on the size of your tables too. 

Databases with window function capabilities (practically anything else than MySQL) will help you with queries like "time between commits". I'd personally recommend PostgreSQL which is great for analytical queries as well.

Document stores and key-value stores are not meant to be backends for serving analytical data retrieval. You might gain some performance on read/write operations but since your application has to do the heavy lifting instead of the database the number of operations increases significantly. So with those it might even be slower at the end. 

How you represent that data at the end is more of a business questions than technical. What your users want. Do they prefer excel sheets over for example an internal websites where they can check? Google Sheets might be a middle ground there. Just an idea.