I killed a couple using the security target plasmid. In fact that's how I got past Peachy on my first try. You still have to know the levels really well in order to lure the Big Daddies into proper position. But you are right, the second half of the game is much easier than the first half.
Survivor mode is hard only if you play it like a normal shooter. If you use the level design to your advantage it's way easier and the mode actually forces you to play the game in a differently. As a result the game feels entirely fresh even though I know exactly what's going to happen next.
EDIT: As a matter of fact if you don't hack the security camera and just use the plasmid on the Big Daddy he doesn't even recognize you as a threat. Hitting him with the plasmid isn't an attack action apparently.
