The level curve in these games suffers because it tries to accommodate the relatively open nature of Johto.

For example, when you arrive at Ecruteak, you can choose to pick up Surf and fight Morty immediately, then go west to clear out the routes between Ecruteak and Olivine, the lighthouse, the sea route of trainers, the Cianwood gym and beat up Jasmine. Then upon going to Mahogany town you wonder why the Rocket grunts in the hideout have as low as level 17 Pokémon.

But alternatively you can also go to Mahogany immediately after beating Morty and ignore the entire western area for the time being. You just need to be able to Surf. That's why Pokémon and trainers on both sides of Ecruteak seem low level when you go to whichever one you choose last. They didn't want you to wander into a route full of trainers way past your level.

Now, obviously I want to have both a good level curve and a fairly nonlinear region to explore, but let's say you were forced to pick between them. Would you rather it was like GSC with nonlinearity and a weird level curve or like BW with a great level curve but a linear region?