> argue vocally with me in a meeting stating that "500 JavaScript requests is not a problem" for a single page

Where's the benchmark or at least the numbers? If not, that's not proof of anything. Nothing to argue about. I'd just laugh.

> You can't win against cargo-cult coders

You don't need to. Unless you're not in control or don't have influence then whatever. It shouldn't be about "winning". It's either some vote (hence influence) or there's a process e.g. PoC with backed numbers.