The thing is, the tax rates only matter if you are successful. Well, mostly. You mostly only pay taxes on profit. (there are exceptions, like payroll taxes, but those are mostly federal.)
I'd be happy to promise to pay a billion dollars if my company ever has more than two billion dollars on hand, if paying that billion makes it even slightly more likely that my company will become that successful in the future.
Face facts, as a friend used to say, your company will probably fail before it makes enough money to pay significant taxes.
And money on the upside? it's got diminishing marginal value. Making promises to give away some of the upside, if it gives you a better chance of getting to the point that there is a significant upside, often makes a lot of sense.
All that said, complexity matters a lot. I mean, until I start making money, I don't really care what the tax rate is - I'm not making much money, so I'm not paying much in taxes. But I'm paying my accountant, and even then, my accountant makes me think at least a little about taxes. And taxes are super complex.
When your company is small, you will spend more money figuring out how much to pay than you will spend on actual taxes. Complexity is a cost even when you are small and posting small profits.