Here is a fun trick. The tethers are predictable. Starting from the first tether the first 2 cardinal CCW blackholes will spawn tethers. You can literally move Exdeath as soon as the first tether spawns because you know where the tether will be.
When the tankbuster is happening, there are no black holes. There is nothing else happening in the fight. If you get hit by the tankbuster no amount of strat changing is going to accommodate for a lack of paying attention to what's happening on the screen.
I have yet to die a single time to being put to 1 hp because the delay is gargantuan. They stop auto attacking because otherwise it would be really bad game design.
Moving out with TIL as tank is not an issue and actually better than potentially a melee losing uptime. Meanwhile when I drag the boss out everyone gets to maintain uptime.
All I see is that you never tanked Black Hole and are just parroting something that someone else told you.