I work with large ecommerce sites (mainly US, UK & EU), for most of them around 75% of visitors are on phones and it’s pretty much the same picture for every consumer facing site I work with.

There’s some variation depending on the demographics e.g. sites with a large audience amongst the older population tend to have more tablet, and laptop visitors.

You can check the mobile vs desktop split for most sites using the Chrome UX Report

You say my logic is flawed but too many sites are designed with large screens in mind and then retrofitted to mobile with poor outcomes for the user experience