It should not be possible for a single person to own 8% of the company the size of Amazon.

If you're starting from scratch, there are many ways to do so. For example, make issuing corporate charters contingent on being employee-owned - so if the company grows, so does the number of owners.

If you're starting with an economy with extreme concentration of capital to begin with, gradually ratcheting up progressive taxation on such concentrated capital seems like a straightforward way to force the owners to spread it around.