Technically, you're incorrect.
Basically, the fire type is awesome, kicks ass and has few resistances to fire.
This would generally make the game easy for you.
Water, has only 2 weaknesses, but a lot of the time they're stuffty like Mudkip. Mudkip and its family have only one true weakness, but they are so badly balanced, they suck. Feraligatr was a physical water type. back in the day, all water types were special. His only good move would be Thrash. This would be normal difficulty.
Grass. With many weaknesses and all the bug and flying pokemon generally at the beginning you are forgeted over royally until you are able to get your grubby hands on another pokemon. This is hard mode.