It's common to see a comic quality increase because the artist gets better over time.
Once you reach your peak you can create consistent art. Of course this all depends on what you consider 'Good Enough'.
Given that comics are in a way similar to cartoons:
Take Adventure Time for example, it's extremely consistent because it is an animation, but sometimes the quality or look can change. Johnny Test is one that changed from hand drawn animation to flash animation. People weren't happy about that change. Why? because the animation had already developed, grew, and established a style that became consistent and then they changed it.
When is it done right? Pokemon and Pokemon Sun and Moon. Clearly the style has changed but the important thing here is that it did not change halfway through a season.
Here's a consistent quality comic