I really don't think you can create a bad sleeper. I've got 3 boys my first was hard to get to sleep, didn't sleep through the night until he was about 2 spent a lot of nights in bed with me. Once he was asleep he slept through pretty much any noise.
My second was awesome from day one, self settled,slept anywhere, and slept through anything.
This one, my third, is terrible still wakes between 5 and well I don't count any more through the night and wakes at the slightest sound, a light switch, door knob squeaking. I always have music playing in the room while he sleeps so that other noises around the house aren't so apparent to him.
I honestly think they are what they are

I'm also with the others about capsules, it's best not to leave them in too long anyway, it's not just thier little developing spines, but their heads. They can end up with flat spots and become a funny shape from lack of head movement.