It depends on the role that the Pure Mortals fill in the party.
I find that casters tend to spend their highest skill slots on Conviction, Discipline and Lore, so their combat skills (Athletics, Fists/Guns/Weapons) and Social Skills (Rapport, Empathy, Presence, Intimidation), tend to be lower. Pure Mortals can't sling spells, but they have better options to shoot, punch, charm, have more contacts and/or be wealthy with a decent Resources skill.
There are two Pure Mortals in the current Montreal-based game I'm in, along with a Gargoyle (a la Disney cartoon), a White Council Warden, a Summer Court Changeling (modeled on Poison Ivy from Batman), and a Svartálfar Dwarf blacksmith that can craft magical items.
My character is a former SWAT cop turned detective, so he's got a focus on combat skills (Guns, Athletics and Fists at Great or Superb and technology skills (Hacker and Demolitions stunt). He has access to some decent firepower (body armor, fully-automatic rifles) when he needs it, and while he isn't as powerful in a hand to hand fight as the Gargoyle, or as powerful as the Warden's Force 4 to 6 evocations spells, he rounds out the team.
The other Mortal in the group is a coroner, and while he isn't as combat capable as my detective, his lore, knowledge, social, contacts and investigation skills are impressive. In many ways, he's functions like Giles did in Buffy, where he either already knows or can easily find out what we're up against. Technically, though, he's no longer a Pure Mortal sicne he was given an Item of Power as a Gift (a pair of sais that improves his HtH melee skill and lets him speak to Ghosts). He's not that great in combat, but the player is pretty resourceful and finds ways to use the environment to his advantage (not to mention the Fate Points he gets from the higher Refresh that he has compared to the rest of us).
I really like having Pure Mortals in the group and find that it adds to the sense of discovery about the supernatural.