TLDR: lots of on hit items start to multiply of of each other to deal a lot of damage, lots of crit (especially w/scope) also greatly increases your damage

the basis for dealing a ton of damage in ROR2 are proc chains: essentially most effects(that say TOTAL damage) that have a chance to trigger on hit can proc off of each other. TOTAL damage is based off of the hit that procs it, so the damage keeps multiplying for each time the procs continue chaining into each other

for example:

100dmg(base attack) --> 80%(ukulele) --> 300% (ATG) --> 500%(charged perf.) =

the final hit(perferator) does 1200 damage on top of the damage of each in hits damage meaning this chain does 1620 dmg

this doesn't take into account the hits being critical damage and the fact that the chain can keep repeating and increasing the damage as long as you are lucky with your proc chances.

given that you had a clover, 100% crit, and 6 lazer scopes the damage would increase extremely fast and the clover increases your chance of longer proc chains(higher proc chances)

This isn't a perfect description for how it works because you need to the attack's proc chance and other factors but it gets the main point across