Yes it is harder to get the kill in core, which also means it is harder to die
And yet it is easier to get the kill in HC, which again means its easier to die
So really those just cancel each other out. But what does make it seem easier and more unrealistic are;
Core Hardcore
Health comes back. It doesnt
Seeing where team mates have just died. You dont
Knowing when to reload Dont know
Knowing how close to a score streak you are Dont know again
Shoot where ever, wont team Kill Got to be careful
Never get team killed Happens very often
Know where team is all the time You dont
May be more but need to get ready for work so will leave it for anyone else to add more in. Or why hardcore is easier than core, other than its easier to kill which is the only one i ever seem to hear.