Fix as in bring back 6v6 because of the obvious terrible things that 5v5 has caused (Tank Counterswap Limbo, unkillable juggernauts, widow, non role queue bs…)
A fourth class that focuses on area control, peel and pressure to play alongside a main shield tank would do wonders in fixing the balancing issues that caused 6v6 to be removed in the first place.
Many ‘offtanks’ translated terribly into the 5v5 solo tank format, and made their main objective of applying and relieving pressure from your other tank impossible because they just don’t exist anymore. I personally stopped playing tank since the switch because it’s physically impossible to do necessary tank duties without sacraficing another. Why would I bother matrixing my supports if I lose all area control for turning around? Why would I bubble a teammate when I could double bubble myself and press W?
Dva, Roadhog, Zarya and Doom and JQueen would be great candidates, balanced to have lower health than their main tank counterparts in exchange for their superior damage, mobility etc. Having a buddy to do some of the work for you and cover your weaknesses would do wonders for everyone, not just tank players.