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I know Whitney isn't the second gym leader, but
The second gym leader tends to be one of the hardest fights in the game. It usually boils down to you having options not strong enough while the gym leader has evolved Pokemon. Shoutout to Bugsy for being the only true exception to this rule; if you can't beat up his Kakuna and Metapod, rethink your life choices. And by that point, you have a ton of options in bug-resisting Pokemon who can deal with Scyther.
For example, if you didn't use Bulbasaur or Oddish, you're pretty much screwed at Misty. Pikachu can maybe get a Thundershock in there, but it certainly can't take a hit from Starmie.
Other 2nd gym leaders tend to vary in terms of difficulty, though. I certainly wouldn't put Lenora on the same level as Brawly or something.