I feel like the deciding factor might to do with team size, skill, and cohesion as team. Having a smallish team makes it possible (although not easy) to have a team that are all high performers. And that team can easily outperform one 2x-5x as large if not more, because there is a large communication overhead to scaling to more people. If you have competent people who "just get" each other, then communication flows and doesn't actually take up much time.

The technology choices follow on from this. If you have a smart team, then you can pick technologies that solve the problem most efficiently, rather than the lowest common denominator that everyone will be able to use, or what's most fashionable (you see this in every field: the "good" people are often following trends or best practices (and doing it well), but the very best tend to have a much more nuanced judgement. They know about the latest thing, they'll use it sometimes, but they keep their own council, and they're not afraid to go off and do something unorthodox if it makes sense for the situation they're in.

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Side point: Incidentally, React is actually on my list of go-to productive boring technologies. It's definitely overused (despite building React apps in my day job, my personal website is built with Hugo, and a lot of sites would be better off with server-rendered Django/Rails/Laravel), but where you need that complex client-side interactivity I think it's the generally best tool for the job.