Apologies- I was looking for the word "benefit". I'm not a native English speaker and sometimes I get word-blocks like that, where I just can't find the exact word I want.
The questions you ask though, work with both "wellbeing" and "benefit". If I understand the first one correctly, you're basically asking: if people are buying a product, who am I to arbitrarily decide that it's not beneficial to them?
Well, of course there is no completely objective way to determine what is "beneficial" to people. However, individuals and societies make decisions like that all the time, because decisions have to be made about what's good and what's bad for people and for members of the society. If there's no way to objectively rule what's good or bad, then we just use our morals and our cultural bias and wing it- and hope that our subjective decision is ultimately close to the goal of making things better for most, rather than worst.
Here's an example: opiate use. Opiates are addictive and damaging to the social life and the health of addicts. Most nations basically ban them except for medical use. We could argue that, if people wish to pay for opiates and are happy with their use, then who are we to say that they are harmful, or in any case not beneficial to them? Well, it's not a cut-and-dry thing but, most communities seem to have -subjectively- decided that opiates are harmful and therefore should be controlled. You're not likely to see a startup disrupting the opiates market to make the world a better place becoming very popular, any time soon.
The alternative to attempting to use one's moral compass to decide what's beneficial and what's harmful, is basically to wash one's hands of the whole question, hiding behind the impossibility of absolute moral evaluations. Which may be rational- but not reasonable, or responsible.
How do you count the "net benefit" I'm describing. In this case, because we're talking about technology, there are some objective rules, namely the contribution of the technology to environmental damage. For instance, cars take you places, but they also contribute to climate change and general atmospheric pollution. In fact, here, the need for mechanised transportation is the intangible value and the environmental damage is the measurable one.
Why shouldn't the change fulfill a need that didn't exist beforehand? Because then the change is hard to measure. Air travel changed the world, sure, but at the beginning the difference to speeds with then-fastest modes of transport was probably small. We can look at air travel today and say "it changed the world" but about 200 years have gone by since air travel became a possibility and the world has changed anyway. It's hard to tell exactly how much it changed because of air travel and how much it would have changed without it.
What is meant by "adequately"? This again is about looking at changes that are easy to measure (and to agree on). You mention people changing providers. For me this is a very difficult change to evaluate (and many of the people who change providers probably do so on spurious grounds, like advertisment, anyway). We had telephones before we were able to carry them around in our pockets and the same goes for computers who can also make phone calls. Why is it so important that I can now carry a small phone - computer in my pocket? How has that benefited me, and does the magnitude of the benefit justify the economics of making those devices?
So basically what I was driving at is that it's not enough to describe a startup as "changing the world"- because you can change the world by tiny degrees, without really benefiting anyone and even cause some harm in the process. Just speaking of "change" is not enough to justify such investment in tech, let alone the self-aggrandising marketing of startups in the Valley. It has to be a big change and it has to be the good kind of change, or they have to tone down their advertisement (or look a bit silly).
The point of the discussion I guess is to what extent "changing the world" is marketing and to what extent it is a reasonable claim to make.
Of the examples you give of startups (etc) that changed the world, I would agree with two: Wikipedia and Coursera. The rest, to my mind at least, are companies that primarily benefited themselves and the change they brought to the world was not really necessary. I hope my criteria -and my clarifications to them, in this comment- are sufficient to explain why I think so.
Thank you for taking the time to reply in such detail.