Building something _different_ faster/cheaper than a competitor is not really the same as rebuilding the same thing with a fraction of the people. In the past when I've seen the claim "I could rebuild this in a weekend" it's literally calling into question why so many engineers were needed to build _that thing_, not something else.

More specifically, new entrants (and especially so in new categories) regularly get the luxury of extended time to iron out issues, create a better UX, find all the edge cases, invest in internationalization, distribute to multiple platforms, integrate with other systems, address security issues, and more. These tend to be exactly the kind of things that make recreating the incumbent products hard.

If OpenAI continues on its current trajectory, it can easily end up with a team equal to or larger in size than all of Google working on search.