The trouble with "investments did better" is that they did so in considerable part due to 40 years of trickle down economics that swung the pendulum away from labor and towards capital. The pendulum is slowing, so that trick is extremely unlikely to work twice. If that's not concrete enough for you, we can talk about what it would take to swing the pendulum as far in the next 40 as we did in the last 40 and this thought experiment will make it obvious that this approach makes the social security trust fund look like an exercise in sustainability.