Yeah, attrition. Relying on quantity of resources rather than intelligence, or quality of challenge.
Always make the final boss (with no particular weak points) a matter of shooting him until he keels over, then a quicktime event. Repeat. On harder difficulties, take this, but make it three times longer per level.
That reminds me of the opposite, actually, and that makes me think of the original Syphon Filter. You go through all these levels and all these bosses, you're getting head-shots, you're sniping, you're blasting through enemies, you're... generally trying to figure out where to go next... and eventually you get to the final boss. If I recall correctly, all it took to kill him was a gas grenade. It's the last thing you'd think to throw at him, but if you did, it ended really, really quickly.
And that is neither attrition, nor a really acceptable challenge. It was just anti-climactic.