As a 109 stick, I'd like to say that firepower is more of a problem than many would intrinsically think, the G-6 and - 14 packing the equivalent of 5 . 50s. As loon says, the issue is more of doing damage quickly, than an inability to do damage.
This is a particular concern for snapshots, where you might very well be physically incapable of getting enough rounds on target to kill your opponent. This is a bigger problem for the 109, since it tends to get fewer chances to saddle up and keep guns on an enemy, but might be mitigated by the fact that the Yak -3 will be more of a maneuver fighter than an energy fighter.