I mean, if we want to argue about definitions, personally, I like Steve Blank's:
"A startup is an organization formed to search for a repeatable and scalable business model. The goal of your early business model can be revenue, or profits, or users, or click-throughs – whatever you and your investors have agreed upon. Most startups change their business model multiple times."
I disagree with the idea that a "startup" needs to be "optimizing for growth at all costs" - as you say. I think this is actually a rather dangerous approach because growth at all costs is how we get things like Ponzi schemes, WeWork, and other abusive organizations.
Your comment also seems to imply that you can't do anything meaningful if you don't have/raise money. This is simply not true.
That was a short answer, of course it could be refined :).
This part of Steve definition is for me the most fundamental: "The goal of your early business model can be revenue, OR profits, or users, OR click-throughs – whatever you and your investors have agreed upon".
When bootstrapping you cannot afford to have a business model that can generate anything else than revenue. Except if you optimize for time while having another full-time job for example.
I was not at all implying that you can't do anything meaningful if you don't raise money. But again it depends what you mean by meaningful.
If by meaningful you mean developing a product / idea that will completely disrupt an industry or the way people live (think Tesla, AirBnB, Apple & co), I'd argue that 99% of the time, people with that ambition will use the VC way.
If by meaningful you mean building a strong business, generating millions of $ and creating hundreds of jobs (think BaseCamp, MailChimp, ConvertKit), I agree that raising money is not mandatory.
But I stand by my point, if you want to change the world, you should probably aim for the VC road.
Steve Blank's definition is not widely accepted in silicon valley. You can argue about what you'd like startup to mean, but what startup means to most silicon valley-ish people is a company designed to grow quickly. It's irrespective of investors, or other things.
Growing quickly doesn't mean growing quickly sketchily... it means companies like Facebook who go from nothing to 3 billion people in a decade... something that was much more difficult before software.
Bootstrapping or indie hacking have usually different goals: you optimize for revenue or time spent.
Shortly said, when building a startup you aim to change the world, when indie hacking you just want to change yours.
At least that is why I chose that path 2 years ago :)