Watching this, and yes there is a massive overlap, the big difference between them is that Leary looks like he's trying really hard to be angry and tough, whereas Hicks came across as quite a warm friendly bloke who got incredibly fucked off about things. Leary is really annoying, demanding you to be impressed by him, whereas Hicks is just trying to be funny. Similarly, I always really liked the Hicks stuff about his mum and dad, and growing up - it wasn't cool or edgy or risque, it was just funny.
Re Leary stealing material - this is blatant ("Whining little maggots?") but I'd concede slight WF in that I did stand-up for a couple of years, and whenever the Z-list comics I usually worked with got wound up about someone stealing their material, it was usually because it was the most obvious kind of observational stuff that anyone with half a brain or more would say to their friends, rather than some incredible imaginative leap. Here, if you're going to talk about smoking, then there is a large area of common ground - health warnings, non-smokers, even Jim Fixx - so a certain amount of overlap can be excused.