Is there no use for high temperatures in ovens?

There is lots of use for high temperatures. Especially pizza is the first thing that comes to mind; there is no home oven which can get to the proper temperatures for a Neapoletana (which are above 500 Celsius), but more is always better.

Of course, the salesman will tell you what you need to hear to buy his product, don't listen to him. This still doesn't mean that you should only buy the oven with the highest max temperature; there are badly built ovens which claim to reach 300 Celsius but can't actually do it, in this case you are probably better off with a better quality oven with a lower nominal maximum temperature. It is probably best to compare reviews made by independent test organizations.

He is absolutely wrong. You can't make a pizza properly at 450? / 232?. You can buy a 1/4" / 6.3 mm 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? / 100?, 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? / 482? or so, depending on whether they’re wood-fired or coal-fired.

The salesman is utterly and completely clueless.

In addition to pizza almost any hard bread will require a temperature of at least 450f. There is really no other way to get a good crust on bread.

Also it is work noting that if steam is required there are oven designed for baking which include steam jets as well as the ability to reach temps in the range of 550-600f. However if you are going to do a lot of steam cooking I would not advise doing it in the oven.

As you suggest: the sales person was uninformed. Maybe commission driven.

For pizzas, a proper pizza stone will suffice.

Other: I don't know what recipe calls for blast furnace temperatures.