If you remove the stock market, you end up with over the counter or even worse total back room trading of company stock

The whole point is that there slowly becomes no such thing as company stock. A precursor step for this is a requirement for all new companies to be employee owned non profits/coops.

We need a ban of companies buying other companies. That takes care of mergers.

However the real problem is the lack of proper high taxes for the wealthy. That has to change, so the wealthy can loose their wealth more easily.

We need all of the above.