I think you’re the first person to address the real reason that this argument (like so many others) persists. Semantics. I think everyone here can agree that Gravemaker is better than the average hero. They differ in where they draw the line differentiating between merely “above average” and “overpowered.”
I don’t feel strongly enough to argue either way, however I will say this: if any hero is so strong that he/she/it becomes the default option then, in my opinion, they are in need of a fix. Players should have choices in who they fill out their teams with. Gravemaker’s overwhelming usage in the top 100 suggests to me that he might be in need of a fix.
What I’d really like to see though, in terms of data to determine his OPness, is what percentage of players with 4/80 gravemakers are using them on their defense teams. I sometimes wonder if the only reason he’s not used on more teams is because they don’t have him.