I drew up a career soldier to illustrate some of the math for the use of Burst Fire.
Career Soldier, Strong Hero 3/Soldier 3, CR 6, Medium Humanoid (human), HD 3d8+3d10+12, hp 45, Mas 14, Init +2, Spd 25 ft., Defense 22 (+2 Dex, +6 tactical vest, +4 class), BAB/Grap +5/+7, Atk brawl +8 melee (1d6+3, nonlethal) or rifle-butt +7 melee (1d6+3) or M16 +8 ranged (2d8+2) or burst fire +4 ranged (4d8+2) or frag grenade +7 ranged touch; S/R 5 ft./5 ft., SV Fort +6, Ref +5, Will +3; AP 3; Str 14, Dex 15, Con 14, Int 10, Wis 13, Cha 8
Occupation: Military (bonus class skills: Hide, Survival, bonus feat: Personal Firearms Proficiency)
Skills: Nah, this is just for the math.
Feats: Advanced Firearms Proficiency, Armor Proficiency (light, medium), Brawl, Burst Fire, Personal Firearms Proficiency
Talents (Strong Hero): Extreme Effort, Melee Smash.
As you can see here, a soldier using Burst Fire (+4 attack bonus) has almost no chance of hitting Defense 22 (10% chance, assuming no range or cover penalties), and even with a normal attack has a 40% chance of hitting.
At higher levels this is less of a problem, since Defense does not scale as quickly as attack bonuses (unless, perhaps, you're a Fast hero wielding a heavy melee weapon).