When I read this headline, I interpreted it to mean Jack owns 28.3% of the shares, but that his class of shares has greater voting rights, and so he has 75% of the votes (a majority - similar to Zuckerberg).
However, that's not what the author means by "control". He means the chance that a shareholder vote goes Jack's way, under the very large assumption that every other shareholder votes independently at random.
That doesn't seem a very meaningful statistic, especially if there are other groups of shareholders with shared interests (for example VCs may be more likely to have goals in common, and would be likely to vote their shares on a big issue together.)
75% is the number of possible situations in which Jack Dorsey could single-handedly control the outcome. That's not necessarily the number of plausible or actual situations that will arise.
Sorry for the confusion, terminology around this issue can be VERY confusing. The word control in particular is nearly always abused.
Control is itself an objective number without assumptions beyond a shareholder-list / Cap-table. Control is literally the percent of all possible outcomes in which the result of the vote/election is decided by the shareholder's vote.
In the link you will find a second graph, in which I give the chances of winning a shareholder vote. Here there is an assumption that each shareholder is as likely to vote one way as another. There is no doubt it is a softer number, but I report it because people can understand what it means much faster than control.
Now these issues of psychology and feelings about particular issues can be accounted for, as you can imagine its necessary when working on the activist situations we cut our teeth on, but there we generally have public statements about which way particular shareholders plan to vote, or how they feel. When looking at a founders long term control, its best to leave out these issue. Less good information is better than more so-so information.
If you want to know a about founders ability to do something specific that would polarize shareholders around common interests, such as sell the company at a price that is personally rewarding, but not great for the investors, that calculation can be done. I just think it should be thought of separately from a founders general control.
terminology around this issue can be VERY confusing
You are not making it any simpler by redefining "control" in this theoretical way. You are making some very naive assumptions about independence: you'd be much better off treating the investors as a single voting bloc, which is what the usual sense of "control" assumes - and if there are multiple founders you should assume that serial investors are very sophisticated at splitting them.
A good followup would be to go out and actually measure the distribution of voting outcomes rather than making a strong claim based on the most tractable assumptions you can find.
To be literal, the only thing that a shareholder 'controls' are the votes that their own shares provide. They may be able to influence the votes of others, but that by definition is not control.
What you've defined in the second paragraph is 'the likelihood that the shareholder decides the outcome of a vote'. You can call it control if you like, but don't make the mistake of assuming it's a very intuitive description of what the metric describes.
However, that's not what the author means by "control". He means the chance that a shareholder vote goes Jack's way, under the very large assumption that every other shareholder votes independently at random.
That doesn't seem a very meaningful statistic, especially if there are other groups of shareholders with shared interests (for example VCs may be more likely to have goals in common, and would be likely to vote their shares on a big issue together.)