IMHO the easiest solution there is to lean more on auto attacks persisting through casts with the ability to crit whilst also giving bosses short cooldown non-telegraphed tank busters and cleaves again.
Kaliya from Coil T11 during prog was a great example of how bosses should hit. It wasn't the hardest hitting boss of the time, but you needed both tanks to soak those cleaves initially and it was nothing like as predictable as what we have now because the bulk of the damage didn't have a huge long telegraph announcing it's arrival.
https://youtu.be/1WwRDVQotgo?t=15