Akusa202 dosen't say "our dmg come from BoS" but "come from DURING BoS"
Sure, HB is our first source, but during BoS we put everything, pot, pof, trinkets, nuke etc etc etc. So during 30-60 sec we will do SO much, from every of our abities but because we put everything at this moment.
for example, my HB should tick around 1mio crit. when i'm Breathing, with all the sh*t. Every HB crit is aroun 2.6-2.7 mio :/ That's why this moment is important.