I live in a poor Southeast Asian country.
People with small data plans don't use data from efficient websites, they use wifi which is omnipresent.
30GB of data on a monthly plan is $3.64. Which is about 4-6 hours of minimum wage (minimum wage is lower in agricultural areas).
But more to the point, people don't use data profligately like in the West. Every single cafe, restaurant, supermarket, and mall has free wifi. Most people ask for the wifi password before they ask for the menu.
I've never seen or heard anyone talk about a website using up their data too fast.
It honestly sounds like a made up concern from people who've never actually lived in a developing country.
People here run out of data from watching videos on TikTok, Instagram, and Facebook. Not from website bloat.