He is absolutely wrong. You can't make a pizza properly at 450°F. You can buy a 1/4" piece of steel, put that under the broiler for 30 minutes, and then put the pizza on that. It will cook in approximately 2 minutes, which is what you want. A home oven typically cooks it for 7 or 8 minutes. At that temperature, the dough becomes much drier and the proteins in the cheese become completely different. You want super high heat to be transferred to the pizza as soon as possible. That provides the spring to the dough, making it rise super fast and cooking completely before it dries out. That gives you a crispy crust with a tender inside and big bubbles. It also melts the cheese so it does not “break” and separate the curd and whey.
You can cook many things at a super hot temperature, particularly if you have a convection fan.
The thing to remember, however, is that air is a bad transmitter of heat. You can hold your hand in air that is 212°F, but you can’t put it into a pot of boiling water. So for pizza or any kind of baking that you want to do very quickly, or making something like fajitas, steel is a good transmitter of heat. Something like a pizza stone is OK, but those are better at storing than transmitting. They work in commercial ovens because those get to be 900°F or so, depending on whether they’re wood-fired or coal-fired.
The salesman is utterly and completely clueless.