I agree that this is the biggest jump. But, some of the most "lasting" characters (Pacman, Mario, Donkey Kong) were created prior to gen 3.
Pac-Man, Mario and Donkey Kong were created in arcades and not on home consoles. I don't really consider arcades or computers to be part of the generation system.
The Atari 2600 was not really capable of creating a character with distinguishing features. Pitfall was a character created on the Atari 2600 and he doesn't really have a discernable face. Mega Man has a face. Having a face means now this is a distinct and recognizable character. The Atari 2600 did actually have a version of Donkey Kong, but the graphics are so bad that Donkey Kong is not even recognizable. I guess Mario is ok, but this should show how hard it was for the 2600 to make discernable characters. Does Donkey Kong look like a gorilla?
Here is the NES version of Donkey Kong. He looks like a gorilla. Note that it was released in 1983 while the Atari 2600 version was released in 1982. Programming skill for both games would be about the same. This just comes down to the graphical capabilities of both systems. Donkey Kong actually looks like a real character.
This was a launch game on the Famicom. After several years the character modeling on the NES/Famicom got better. Think of all the Punch Out characters. They all seem to have a distinct look and personality. There is no way the Atari 2600 could have done anything like that. The NES was the first home console where unique characters could be created.