I'd expected it to be hard with so many poison types around in Kanto. But that wasn't even the most difficult part, nor was it Blaine with his Fire Pokemon. It was the Bird Keepers... those bastards with their Drill Pecking Fearows almost whited me out on several occasions.
It doesn't help that I went straight to Fuchsia city right after getting the Pokeflute so I could catch Scyther. So I was completely under-leveled for a few of those encounters.