I think the overall issue is balance. Not every character necessarily needs their whole run dedicated to a singular, long-form storyline, but if you're going to go there, it would be wise to at least pepper in the occasional one-and-done for a breather here and there. In fact, I would argue that the longer and more involved and complex a major storyline in a character's ongoing saga is, the more "breather issues" it'll need for balance, so the character and the audience aren't too weighed down in the middle or by the end of it. That being said, while it is generally a good idea to have a firm idea for both the writers and the readers about who the character is and why they do what they do, the writers don't always have to make a big, dramatic event (in more ways than one) out of it, and execution ultimately matters more in the long run than intent.