You're not wrong but I think this exchange might have gone differently if the tone wasn't so incredulous from the start. Perhaps something like this:

"I know JavaScript is assumed to be universal these days but since this is really just text it would be great if it just displayed the raw text as a fallback for when JavaScript wasn't available."

I know it's kind of silly but how we present something can dramatically change the response. But in fairness sometimes a direct and plain explanation for why something is bullshit is the only way to get things noticed or done too.