Is there a way to track text-bytes changes Drupal nodes?
Yes, all one needs to do is look at the field_data_body table and compare the byte count of body_value between revisions to get this information.

In fact, this would probably make a good patch for the Diff module which alters the node Revisions tab to an interface pretty similar to MediaWiki. The only thing missing is the core of your question, a comparison of byte count between revisions.