The flip side of this might be to increase weapon power a bit? It seems a bit odd to me personally that most mortal weaponry is only between weapon: 1 and 3.
It's probably more accurate to say that the type of mortal weaponry that appears in noir type stories is between 1 and 3. Thinks like crew served weapons, recoilless rifles, and anti-tank missiles just don't show up.
As for comparing mortals to evokers:
Non-PC class, but competent, mortal gunman:
Targeting 3, weapon 3 (assault rifle)
Non-PC class evoker:
targeting 4 (discipline 3 + focus item), weapon 3 (conviction 3)
10 refresh wizard, some twinking (4 points of refresh spent (evocation 3, refinement 1)
targeting 8 (discipline 5, +1 foci, +2 refinement), weapon 6 (conviction 4, +1 foci, +1 refinement)
10 refresh gunman (1 point of refresh spent, (gun targeting +1 stunt)
targeting 6 (guns 5 + targeting stunt), weapon 4 (anti-material rifle / grenade launcher (zone wide effect))
and if you'd allow a +1 gun damage stunt to give the gunman another way to sink refresh into guns. Or he can just spend his spare refresh to up gun rolls during the adventure.
And, depending on how combat scenes tend to run, the metal stress limit of evocation can come up very quickly.