Insane is really not how I'd describe Gyarados
Although PSA initially struggled to make much headway within the TCG community, it received a massive boost with the dot-com bubble of 1995 to 2000
Now, over 20 years later, we have thousands of cards, covering over 900 Pokemon
If you are just playing the card straight up, its kind of a build your own Thoughtseize. That said, it was always particularly powerful that you could ensure your opponent doesnt have the card that can stop you, since even if you missed, it meant they didnt have that card
Each section will be broken into what Im going to call mandatory and flex. Cards in the mandatory are cards that I think should be in the deck 99% of the time (I suppose there technically can be metagames where you cut them, but I personally havent encountered them)