Thats just an example,
with rooting damage taken as 100 ,
Heres the actual =
E damage lvl1 = 150
with SC = 150 150 150 = 450
with FS = 210 210 210 = 630
Difference in Damage = 180
But at lvl1 , u dnt get the SC , so lets check at lvl20
E damage lvl20 = 316
with SC = 316 316 316 = 948
with FS = 442.5 442.5 442.5 = 1327
Difference in Damage = 379
379 = roughly extra 10% to 12% of most assassins hp PER casting of E, and I can cast them every 4 to 5 seconds 
But I agree, i can spam those n hit people in bronze n silver, later it wont work,
so i shoudl enjoy this mad deckard build while i can
And keep the “BRONZE” rank in mind when u suggest me how to improve it 