On an individual level: Yes. Even a thousand (median) retirees don't own as much as one billionaire. But in total: All the old people together own an order of magnitude more assets than all the billionaires put together. Because there are so many old people. A large part of it will be their homes of course, but there's still a metric fuckton of stock in there via retirement funds.

Go look at Amazon for a particularly egregious example of a corporation that abuses its workers. One would think Jeff Bezos owns a huge part of it, but actually he owns about 8% of it, being the biggest individual shareholder. 75% of float and 68% of all shares are owned by institutions. Then look at the biggest institutional holders: They're all companies providing ETFs and mutual funds. Most of that (obviously not all) is retail investors and retirement funds, as a lot of rich people find such fund investments boring (average ~10% annual growth long term is not enough when line must always go up). Thus a large proportion of the wage theft by Amazon benefits people investing for retirement, or that have already retired.

Some economic systems fix this by giving every worker and every retiree an amount of money every month and not allowing anyone (retired OR working) to have any investments at all. This puts an upper limit on how much any individual person can own and spend. It affects retirees more than workers because retirees are the ones who have had time to amass wealth in their working years. There's less inequality, but the downside is that no matter how hard you work, your retirement will be exactly the same as everyone else, including those who barely work.

There's no perfect answer. Under capitalism, workers will naturally feel that the ownership class (mostly old people who were smart and prosperous enough to invest, or lucked into a job with a real pension) own too much. Under communism, retirees are likely going to feel they aren't being rewarded enough for the hard work they put in throughout the years. But crucially, neither extreme, nor really anything in between, addresses the fact that most countries' populations are aging, and the lives we've gotten used to, have been based on there being fewer old people than working people. That's why I see only two solutions: We all accept that we have much less (and yes, there should be a wealth cap too), or enough work gets automated that not many workers are needed anymore AND the economic system accounts for it (doesn't have to be communism, but it can't be unbridled capitalism)