Generally, startups have drastically less internal momentum, bureaucracy, tech debt, or politics to contend with and are much better positioned to push fresh ideas, and be responsive to customer needs rather than fitting a larger corporate narrative. But its fair to say that if a startup idea is really just a feature idea (even a really good, well-executed feature idea, like Calendly) and doesn't scale its ambition beyond that, the best outcome to hope for is a buyout, and at worst being built internally by a giant.
On the other hand, its never been easier to start a software business thanks to incentives from the tech giants. Google Cloud is basically free to start up and gain traction with. Granted, there may be downsides to this, but not having to think too hard about infra opens up a lot of opportunities at the same time.