Am I wrong thinking this works?

I played a game today on Spelltable and had all 3 opponents salty because I played [[Apex Altisaur]] and in response to its fight ability, I cast [[Heroic Intervention]] to give it Indestructible and kill every creature my opponents controlled. They think my creature would lose its power with each creature it fights, diminishing its effect. I said it deals 10 damage to every creature until they all die (withholding Hexproof, Shroud, etc).