As for the budget share, a significant part of that is going to be govt-owned corporations that are used as cash-cows, for example the energy production / distribution monopolies, national lottery, Tallinn Port etc. Last month's news - this year they contributed 157MEUR dividends: https://www.aripaev.ee/uudised/2018/04/19/riik-votab-ettevot...
In the end, "regular" companies end up paying less than you imagine. I think it could be a sign that the policy is working - companies are investing into the future and "paying it forward". Or they are doing creative feats like taking out profits as loans to parent companies, which is also known to happen, specifically the big Scandinavian banks here.
Specifically for startups, it is going to make a big difference if you do not need to pay yearly corporate tax at an arbitrary date (in relation to your business) and can a) postpone this until profitability or b) never pay a dime if your idea never pans out. You can even steer your company towards an exit without ever having to think about it.
Many people I know personally only distribute as much profit as they need for themselves. It is not double taxed with personal income tax, so it is spending money already after paying the corporate tax. This has lead to a debate as to whether this actually constitutes "entrepreneur salary" with entrepreneurs therefore paying less taxes than employees (the salary taxes are much higher: http://palk.crew.ee).
That is why for a startup you can "essentially" forego thinking about it. When you do, you know you have made it :)
The question I have is whether you're required to claim a salary (instead of capital gains) as a sole employee of your corporation if you're a full tax resident there.
This might be too specific for HN discussion, but feel free to email me.
https://investinestonia.com/business-in-estonia/taxation/
Estonia's corporate income tax rate is not essentially zero, unless you plan to never distribute any profit. Otherwise it's 14-20%. It would be unusual for most businesses to never distribute profit.
Last year Estonia collected something like €368m in corporate income taxes. Or €283 per capita. Equal to about 4% of their budget. Not a huge sum, also not anywhere close to zero. In the US for 2018, corporate income taxes will be about 5% to 6% of tax revenue (4% to 5% of the budget). The US corporate income taxes collected, broken down on a per capita basis, will be around $650 to $700 for 2018, for comparison.
You can plainly see that Estonia collects corporate income taxes:
https://www.stat.ee/53719
https://www.oecd.org/tax/revenue-statistics-estonia.pdf
The primary unusual thing Estonia does, is not tax profit until distribution.