Taxation isn't natural.
By the way, I'd like to remind everyone: when the state taxes something, the state now depends on that thing for its budget.
> If retail company that has 30% market share pays 0.3% extra from its revenue compared to tiny company with just 10,000 customers, it would probably be enough to even out the field and limit barriers to entry.
If you are really interested in barriers to entry, you can do a thought-experiment (or a real experiment): try to start a business. See where the friction is. And then ask yourself what the barriers were.
Another thought-experiment: imagine if starting and running a business (which includes collecting revenue, paying employees, paying taxes, abiding by the law) were nearly zero-friction. If starting a business had very low artificial friction, then there would _actually_ be natural pressure against market incumbents.