The main difference is that Mac’s main movies are starring Mac, two of which Kieran was in as a minor character, but Kieran is almost always a supporting character or a co-star in the stuff that he’s in.

Also I’d outside of Scott Pilgrim snd Succession Kieran’s works aren’t as successful as Mac’s, Home Alone is still a Christmas mainstay, especially the first two, My Girl is still a hugely successful movie, and the Good Son was probably one of the best child horror performances ever, then you have Uncle Buck and Richie Rich, Saved! And Party Monster are both cult comedies as well, Party Monster was required watching to be a raver back in the day along with Go and Groove.

Overall Mac has a cultural impact far beyond what Kieran has been able to do so far, so Kieran is definitely overshadowed by his brother, but I doubt for much longer, his momentum seems to be building and I’m looking forward to what I see him in next.