The OP claimed only 2-3 people in each company are "responsible" for the success of said company. You do not need to be the only person in the world who can do a job to have some, or even major, responsibility for the success of an organization.
I think you may be misinterpreting what OP meant (or perhaps I am, that's a real possibility). I read that as "There are only 2-3 specific people whose skills and contributions were so essential to the orgs success that the org would have failed without them specifically." Where you might have a front end developer who is technically "responsible" for facilitating millions of online transaction, there are likely thousands of other devs who could have done the same work. Among the 2-3 OP was referencing, there are very few who could have done what they did.
The case I was making is, it takes many people to turn a startup into a unicorn, and many of them are integral and make massively important contributions that, without them, would not have occurred. The degree to which those people are replaceable is difficult to say precisely, as it varies per person and per company, but I don't think being irreplaceable is the bar for being considered responsible. If a fireman pulls a kid out of a burning building, we don't care that many other fireman could have also done the same thing. The individual who did the critical work is responsible.
I have been at unicorn companies with C-suite executives that are clearly useless, or worse, net detractors playing political games that the people under them have to work around to get shit done. I have been at companies where one engineer is single-handedly keeping parts of the lights on, or conceptualizing and architecting critical systems, having an outsized impact well beyond their title and compensation. There seems to be a false idea here that the way companies run is "top down" - ie. the Collison brothers set out all the goals and strategies and products, and then the employees just execute their vision like pawns. Maybe there are companies like that, but I've never seen one, particularly a fast growing one.
I guess I just disagree that the number of people who would be deemed "responsible" for Stripe's success is 2-3. That seems, frankly, unbelievable to me having worked in companies with hundreds or thousands of employees and seeing how many different people it takes to build something massive, innovative, with multiple product or business lines. Not just taking marching orders but exercising their creativity, judgement, expertise, leadership skills etc.
