That mechanic concept is amazing, but the reality is terrible.
Not for the difficulty on itself, but for the:
1) RNG of orbs
2) TERRIBLE hitbox while on midair
3) the unforgiving low timer is a deadly combo with point 2. Why no extending it a bit for normal mode?
4) absence of any visual information about what's happening in the room (really we have to use taco & external tools for timers?).
On my BS pov that always (have to) do G1, that's not a skill check, and that's not funny.
Just to works with fantasy about improvements...
It's a static pattern, so why doesn't the green pop early with a global message like "Reaper of somewhere is beginning his ritual soon, protect him" with a marker on him 10 seconds earlier ? (just as example).
Also, why no 10-sec early information for the greater mark ? (like "Dhuum is channeling power for his big bad greater mark. Be ready!")
I don't see many post about that. Maybe i'm the only one that expect rework on this boss.
My 2 cents