One thing I think people often forget is what that X less Refresh actually means for the Mortal Gunman.
So you can have that Evoker with the Targeting roll of 8 and Weapon: 6, costing at least one mental stress...
The mortal Gunman has the base of the 5-6 targeting roll and Weapon: 3, but is invoking 2-3 or more aspects on the environment, his character sheet and perhaps on the enemy and suddenly you are looking at a 9-12 targeting roll or more.
Mortals have fate points to spend that higher level supernaturals do not.
One thing to keep in mind as a mortal player - think of your Refresh level as your "super power" If you are not spending at least 4-6 fate points between every refresh you are not using the "power" that you bought by being a mortal. Ideally, you would use almost all of your fate points, particularly when you are pretty sure you will get a refresh.
People have a habit of trying to horde resources, and I think a lot of the "balance" issues actually slow down if you encourage mortal players to really cash those fate points in.