Maybe that’s what they want. And not so much “OffTank”, but “Heavies” from the Class Based Shooter genre.
Clearly the vast majority of the players are DPS. And more than half the Tank players like playing like DPS.
And Zen, Bap, and Ana play a lot like DPS.
Maybe appealing to the playerbase they have, is better than trying to appeal to a playerbase that doesn’t exist?
Personally, on the MOBA to FPS scale between LoL and Valorant.
I see Overwatch fitting somewhere between Paladins and Apex Legends. Heading in the Apex direction.