The problem is that you don't usually own 100% in the beginning as a founder. You're most often starting out as a co-founder, split depending on how many co-founders. That means you would have much lower ownership than what you indicate, not only starting out but more importantly, by the end of the 4th round. In addition, you usually need to slice the pie even smaller after series A for employee ownership. So, unless you expect your startup to be a unicorn, you're essentially another employee by the 4th round in your scenario. A well-off employee, but an employee nevertheless as you obey the whims of the VCs who are your bosses.
The problem is that you don't usually own 100% in the beginning as a founder. You're most often starting out as a co-founder, split depending on how many co-founders. That means you would have much lower ownership than what you indicate, not only starting out but more importantly, by the end of the 4th round. In addition, you usually need to slice the pie even smaller after series A for employee ownership. So, unless you expect your startup to be a unicorn, you're essentially another employee by the 4th round in your scenario. A well-off employee, but an employee nevertheless as you obey the whims of the VCs who are your bosses.