What makes you think so?

const bigJSON = '{"gross_gdp": 12345678901234567890}';
JSON.parse(bigJSON, (key, value, context) => {
  if (key === "gross_gdp") {
    // Ignore the value because it has already lost precision
    return BigInt(context.source);
  }
  return value;
});
> {gross_gdp: 12345678901234567890n}

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/parse

I’m not following your point so I think I might be misunderstanding it. If the types of numbers you want to express are literally incapable of being expressed using JSON numbers then yes, you should absolutely use string (or maybe even an object of multiple fields).