When the Heroes of the Storm development team first designed Gazlowe (or Tinker, as he was initially called), the game was completely different than it is now. What heroes could do, how maps were designed, and how the game was "meant" to be played has changed dramatically over the years. So when Gazlowe was introduced into the title back in 2014, his kit worked well for the time period. He could split push lanes, clear mercenary camps efficiently and his team-fighting ability wasn't that bad. Fast forward to the year 2020 (and two reworks later), the development team felt it was time to give his kit another look after his most recent overhaul in 2017.
