Also that this wealth is dependent on value. It's not like having cash. It's shares, whose value will go down if the company stops providing value.
Yes, in this theoretical world where stocks trend down over extended periods of time, I could see this being an issue.
In the fairy farts world of the US stock markets, we don't often see mega corps trend down. That's why every American pension is piled into SP500... Which is really driven by the growth of like 10 companies, tops.
But that's only if they keep generating value. Plenty of companies don't do that and we forget about them. Basing one's worldview only on peak performers is the apex fallacy[0].
[0] https://rationalwiki.org/wiki/Apex_fallacy (I know, I know, rationalwiki)
It doesn't need to hit peak. It just needs to be a good bit above where it was issued. Zuckerberg, e.g., could run this strategy indefinitely, even if meta dropped by 50%. He'll still defer the cap gains until his grave.
Once capital grows large enough it starts being able to bend the fabric of economic space around it. It begins to change rules and accumulate more capital merely because it's so big. This is a natural feature of capitalism. Properly attended to, fire makes steam and runs an engine. Left unchecked, it's a forest fire. Capitalism is like that. It needs moderating influences to keep it controlled and useful and not consuming everything it touches.