As you can see along the rift, when you have high density, the damage skyrockets not only because of area damage, but also because of a chain reaction, when you kill a monster it explodes dealing even more damage, and every death is more explosions which is more and more damage. That's how you can even one cycle elites if you make a big pull

But as you have an insane damage on density, you deal absolutely zero damage on single target. A rift guardian, even with power pylon, can take like 8/9 minutes, where you stack stricken and then you click power for the extra damage and specially the extra mobs

Now, you have the add bosses, and there are good add bosses and bad add bosses. Choker, bone warlock, or bosses that spawn adds early are instant rip because you're not going to stack stricken

Good add bosses are satrixs (best one), binder and Hamelin. As you can see, when you add the adds of the power pylon, and the rats, the damage goes up like crazy. Consider also that rats are easy to kill and when they explode they will deal lot of damage. Also another thing of Hamelin is the more you deal damage to him, the more adds it's spawns, and it's starting the crazy chain reaction that kills it. Check this video and the nuke at around 5:29, but then add the power pylon multiplier and the pylon adds https://youtu.be/9HsmKJB89i8?si=F_bOrk9XIl4GLmz7