I think it's mainly the gun.
Once I changed the hammer spring on the Beretta 92FS i prev had, it made it easier. I have both a HK USP and USp compact (in 9mm) - the Da pulls on them are kinda heavy. But, I keep them cocked and locked, so it's not an issue.
I find the DA trigger on my P99c is not that heavy. Probably the lightest DA trigger pull I have felt on a DA/SA.