Probably is, given the kind of character he is, that seems like that would be his schtick: the cute little tagalong baby (step)brother.
In all honesty, before we were introduced to Rudy on the show, and reading about some of the episode plots that involved him (like taking Abby's wand and getting into trouble with it), I foresaw him being an almost D.W.-esque kind of character: kind of a brat, and a bit of an annoyance to Abby. At first, I was relieved that he didn't turn out to be that kind of a character, mainly because it's just as much of a troperific characteristic for younger sibling characters, and would make Rudy too much of a cliche . . . but now, I'm wishing they kind of went that direction. I mean, he doesn't have to be exactly D.W. level of brattiness, but at least maybe give him a bit of a mischevious streak to make things a little more interesting: not only would that make Rudy himself more of an interesting character, but it could present some further development for Abby as well, putting her into a role of a responsible and somewhat flusterred big sister.
Then again, I know SS has really been pushing the kindness angle in recent seasons, and that really is all well and good, especially with the way the world is today, but as both
@Oscarfan and I have been noting lately, the storytelling and quality of the street plots has been suffering quite a bit because of it - it's almost as if the writers are afraid of conflict, and that's where your story comes from: without conflict, you have no story, and the street plots as of late are more or less just random events and things happening rather than actual stories. And it's ironic, given that SS has two of the original ARTHUR writers now: Ken Scarborough and Joe Fallon, both of whom were notorious for some of those classic, old-school D.W. pesters Arthur and Arthur is about ready to blow his brains out scenarios (Joe especially).
If nothing else, the conflict could be written into the stories in a way that they serve as lessons for kids on how they could handle real-world conflicts. SS
used to write stories like that.