Gargos excels in the one archetype that wants it
Damage easily wins games, and serves as an easy payoff for infinite +1/+1 counter or proliferating combos
The only problem with that strategy, however, is the fact that Hyper Aggro dies pretty easily to steel decks, and theres plenty of steel going around
Illustrated by Jerry Tiritilli Standard Not Legal Alchemy Not Legal Pioneer Not Legal Historic Not Legal Modern Not Legal Brawl Not Legal Legacy Legal Comp
Replacing black with green allows you to play Knight of the Reliquary to tutor up your combo lands and attack with a solid creature
On the other hand, if you are willing to increase the budget just a little bit, playing Path to Exile over Declaration in Stone would represent a big improvement (plus, if you're getting into Modern, Path to Exile is a card you want in your collection anyway since it's a true staple of the format)