The question isn't whether they need more people to make it all work. That's not in dispute. It's the degree to which any of these people are replaceable. If you removed any of the engineers working on the iPhone Jobs would have hired another engineer and cracked on with the project. Maybe there would have been more bugs, or slightly worse features, maybe there would be some things better.

Take out Jobs, and there is no iPhone, or even an OSX to base it on. It took the competition years to catch up, and that's bearing in mind they knew they needed to. Prior to the iPhone announcement, Android was going to be a BlackBerry clone.

Or take SpaceX, nobody but Musk was pushing for first stage re-use. Seven years later no other company has landed an orbital class first stage booster, or seems anywhere close to doing so, and that's with the concept absolutely proven. How long would we have to wait for someone to even try without Musk gathering a team and making it happen?