I find the guns to be perfectly fine.
This is a video game, not real life. It's meant to give everybody a chance. I understand if we're trying to look at it realistically, but is it really that big of a deal?
If you actually know how to be a little more tactical you can take people out pretty easily. Use upgraded melee weapons, smoke bombs, etc.
That's what I rely on. Melee weapons and smoke bombs. Smoke bombs disorient the enemy for a few seconds and can give you the opportunity to either gun them down, or go beat them down. Play it smart, and stick with your team, trying to be a hero in this game never works, trust me.
Just finished my first run through the game. Here are my thoughts:
1. This isn't a shooter. Guns don't play a massive role in the game so don't expect CoD or [insert shooter here].
2. Guns, even the pistols most definitely stagger opponents.
3. The game encourages you to use alternate means (read: stealth takedowns) to dispatch enemies.
4. In those moments where you have to use guns, headshots are an instant kill and save precious ammo. Which would lead one to conclude that you're not landing headshots. Improve your aim.