It's just that the Medicine Stick is one of the most well-rounded and powerful guns in the game, and yes, Raul does use it better than anyone else (maybe even the player character). There's also nothing stopping you from giving Boone the Gobi Sniper and watching him work. Obviously though, some people might prefer a ranged companion. For example, Lily could surely compete simply because she's fast as hell, has tons of health and with Oh Baby!, she also hits for truckloads of damage.

Well of course any companion with a 10 charisma (or high charisma) character would be badass, but it becomes a matter of preference.