Now, all that said, if capital (savings) grows faster than the growth of the economy, those with savings will see their wealth grow at a faster rate than those who rely on the growth of their income. While this is not an extension of Piketty's argument (you can't take an idea that applies to a population and a whole economy and boil it down to the individual like this), it's not an unreasonable conclusion to take and apply to your own life. (Piketty does talk about this on an individual level, but says it's more impactful for billionaires vs. millionaires – though we have limited data into individuals)
Most of us think of investment income as just the cash flow we get from bank interest, bonds, share dividends and property rents, some of which comes via a super pension.  But a more complete view is to also consider how growing the value of your investments can add to your spending potential.  This total return approach generates income from both income and growth to optimise spending from your portfolio across all market cycles, aligning cheap and expensive investments to your goals.