Are you playing with a "Fast" or "Slow" ball? Never play with the "Slow" ball unless you are physically handicapped.
I don't find either one THAT easy. But then, for me, pinball games are a timewaster I like to drop in when I know I've only got a half hour or so to kill before going out, etc.
I love both those games, but I never sit down to a long gaming session with either one.
I don't think Devil's Crush is harder, but there is more to it. Actually, maybe the bonus rounds are little tougher but that's it.
If you want to add a little spice to your Alien Crush gaming, when you get to the bonus round with the skulls and the green things, eliminate everything but one skull. Knock your ball around for a few minutes without eliminating that last skull and you'll get a surprise. Don't lose your ball!