Step one: fill your inkwell with 'Read a Book'
That means that a Giant Growth turns a -1/1 creature into a 2/4 but that preventing the next -1 damage is the same as preventing 0
Their spell and trap support from the GX was incrediblewith their continuous spell Gateway of the Six they could gain nearly infinite advantage to search and summon monsters, and all of that was without counting their synchro boss, Legendary Six Samurai Shi En, one of the first extra deck boss monsters to possess the ability to simply negate spell and trap effects
This isnt a controversial opinion where I come from
That said, the rarity, card art, and popularity of this Pokemon is currently supporting the price, and it will be interesting to see what happens in the future
That said the card would not see all that much more play if were a guaranteed 5 damage every time (counter burn being the only deck that this would be really significant in)