What do they mean by "assets"? Is it securities in the form of stocks/bonds/etc?

If so they own a bunch of bits on a server somewhere that technically represent an amount of goods/services they could never use in 10,000 lifetimes.

If Elon had 10 billion eggs in a warehouse it would be real easy to fix the price of eggs. We could also reduce healthcare costs by making Bezos & Zuck stop going to the doctor 4,000,000 times a day.

The reason peoples labor isn't granting them the goods and services they want is way more complex than just: "the billionaires are taking them all". You could kill every billionaire tomorrow and distribute all their wealth and it would only make shit cost more.

You are so close. The rich don't buy all the doctor visits, they buy whole farms/doctor practices and place a tax paid to them on every transaction. We are switching to a society structured for maximum extraction everywhere because there is so much capital at the top looking for places to park, and why wealth disparity is so bad for a society. The feudal lords got paid on every transaction and with the current disparity the rich are buying their way back to that system.

Poor spend money to survive, circulating through the system.

Rich park excess money in PE buyouts of previously owner owned dental practices, HVAC, rental properties, etc and 'optimizing' for maximum extraction. Some capital is needed to fund new things, but excess turns EVERTHING into rent extraction with barons taking their cut above all else.

More and more of the services/things in life are owned not by the person that started the business, but by the rich whose money 'is just bits and has no impact on the poors'. Rich don't compete for doctor appointments, they just extract more and more $$$ by owning every doctors visit, every practice, every corporate farm. And the poors can't compete. Hence you end up with a feudal system because of the disparity. The rich should have enough to enjoy a good life and to have freed up investment capital in the system to start new things, but not enough to re-convert society back to feudalism where they own all and get paid a percentage on everything, always, just for existing.