Attack and Defense ratings for guns and armor are normalized. But weapons will retain their special ammo type if they have one, and stats like rate of fire, magazine size will remain unique to each gun. For uncommon (green) weapons and armor, any abilities they have (changeable scopes, throw grenades farther, melee hits decrease super cooldown, etc), as well as +STR/INT/Discipline they may have are in effect. With all this in mind, a higher level player will have an advantage in terms of equipment over a lower level one who might not have uncommon equipment. I might be wrong about the +STR part, but when I was playing with +27 INT, I felt my super cooldowns were shorter.
And the higher level you are, the more character upgrades you have access to. You can switch to different types of grenades, improved double jump/glide, and access to different stat builds, Fir Hunter, there is Way of the Nomad and Way of Something Else (I forget the name), but those can give you different levels of speed, toughness, and regen.
As for PVP tips, I found it best to not lone wolf it, and to attack/defend objectives with at least one other teammate. Sure I could win some firefights when soloing, but I lost more often. Headshots do a lot of damage and getting consistent at headshots decreases time to kill by a lot, compared to shooting only the chest. And at least in the Alpha, shotguns were pretty OP. I had to carry one myself to counter it, and it helped out a lot. And know when to trigger your super. Titans and warlocks have supers that can get multi kills easily, especially when you flank. As a Hunter, if I notice that we were losing one of our capture points, I'd summon the Golden Gun just before turning the corner to see the actual point so I can clear it out quickly.
Guns I used in PVP:
Auto rifles, pulse rifles (really good at mid/long range when you can land headshots), shotguns. Rocket launchers were also really good to use, pick up that heavy ammo when you can!
Did you up your stick sensitivity? I found it sluggish at default, but I cranked mine up to 7 and felt I could track opponents more easily.