I don't think evil triumphs more often than not in the 'real' world. But even if I did buy into that philosophy, I tend to think that fiction is about the world we can create, not necessarily the one we've got. So I don't see the need to overwhelm readers with death and destruction at every corner.
I think the Marvel Universe is a place where bad things often happen to good people, but heroism tends to prevail. You look at say, Flash Thompson or Matt Murdock, and they've lived hellish lives. But I also feel pretty inspired by their persistence in the face of overwhelming odds. When you're Flash Thompson, getting out of bad and taking another shot at it is a triumph over evil!
I'm cool with a nice balance. There's no reason that the heroes should get it so good when their supporting casts get routinely decimated to prop the main guy or gal up. No one feels bad for Gwen, but oh no please don't hurt Spider-Man. Heck with that noise.
I know Kevin Nichols through a guy that knows a gal. Small world!
If nihilism didn't take some delight in destruction one might suspect nihilists were an unnaturally morbid sort.