I don’t think I’ve ever seen either 0°F or 100°F used in any way to refer to actually temperature. It’s always defining the scale or comparing to °C. Maybe once when checking for a fever.
What? Are you actually from somewhere that uses F? Because what kind of argument is this? You’re saying that 0F isn’t “really cold”? That’s a very specific take likely based on the very specific region you live in. The vast majority of the world would call 0F “really cold”.
And likewise, as someone from arizona, 100F is hot but not “really hot”. That doesn’t start until after 110 or 115. So in general, out of the entire world, 0-100 is a pretty good range of “really cold” to “really hot”. Only the people who live in the specific places that regularly get much colder or hotter actually care. To most people, it doesn’t really matter if it’s 0 or -10 or -15, it’s all too fucking cold. Just like to you 100 or 110 or 115 doesn’t matter, it’s all too hot.