There are a few heroes that walk the line between Tank and Bruiser and can act as one or the other in a pinch, and I think Imperius can walk this line when necessary.
However, I don’t think he’s classified incorrectly. Tanks have to check a number of boxes in order to be effective in their role, and Imperius doesn’t check some that are fairly important. Some of those are:
- Reliability and consistency of CC
- Ability to survive being focused by the enemy team
Back in the day we also originally intended for Dehaka to be a main tank, and he had a similar issue in that he could reliably take a lot of damage, but his ability to CC was primarily tied to his Drag ability which wasn’t consistent enough to have him be a main tank due to its range, wind-up, and ability to only CC 1 target. I think Imperius falls into a similar category due to the nature of how Celestial Charge works. It’s not quite reliable enough to deter enemies from diving his team in most situations since it has a bit of a delay and hits a small area. His ability to survive damage is also tied heavily to his ability to use Basic Attacks against enemy targets while they have Valorous Brand, which is not as consistent of a way to survive compared to other tanks in our game.
I don’t think it’s impossible for him to be successful in the role, but I think there are good reasons why you don’t see him acting as a tank in most of his games.