This is bad math, not researched heavily but in 2020 discord had 300 million users. 285kb goes a long way with wasted energy and bits flowing through the pipes. I agree generally with what your saying though gzipped sizes are what's being sent some CPU usage somewhere to unzip. less bytes == less waste?

PNG basically includes gzip in the file format, so you're not reducing the amount of CPU used, you're just moving where it happens.

Includes but doesn't always use. PNG also includes filters which can dramatically decrease sizes, especially when combined with compression.

That's why tools like OptiPng basically brute force all the combination of options. Depending on the image content different combinations of filters and compression will get the best file size.