Exactly. Don't use other people's code / depend on their code / services.
But you're wrong about size. It matters. If your code is small enough you host it yourself rather than relying on external CDNs. Risk surfaced reduced. And smaller code mindset leads to less use of dependencies / bloatware like the React/Babel tool chain, so of course this leads to less risk.
But it also makes fools of a lot of people and conventional/fad wisdom, so I'm unsurprised they're unhappy to hear it.
But you're wrong about size. It matters. If your code is small enough you host it yourself rather than relying on external CDNs. Risk surfaced reduced. And smaller code mindset leads to less use of dependencies / bloatware like the React/Babel tool chain, so of course this leads to less risk.
But it also makes fools of a lot of people and conventional/fad wisdom, so I'm unsurprised they're unhappy to hear it.