The breaker exists to protect the wiring. The fuse is being spec'd to protect the equipment. Disconnect is to make servicing it safe
Yes. The wire won't be hurt if it has pretty substantial overcurrent for a fairly lengthy time (a squareD circuit breaker will pass 2 times its rated current for 100 seconds before it trips, and 5 times for 10. That's on breakers that made their name as "quick open"! The relevant UL standard allows longer times. That lets things like incandescent lightbulbs and motors, both of which have much larger startup current requirements than steady state, get going without tripping the breaker. And why motor and HVAC circuits are allowed to have breakers bigger than would normally be allowed for the wire size.), the breaker just has to trip before it melts. The machine, on the other hand, might well be damaged if it draws excessive current, even momentarily, so a fast blow fuse protects it from that. It's also common to install a unit on an existing disconnect that uses less power than the old one, and in new construction, the wiring is often done by someone who doesn't know what was speced, so they often use the largest reasonable circuit breaker, and the fuse in the disconnect is properly sized when the installation is done. All that said, I suspect the reason that lots of chinese mad stuff is still calling for fuses is because the importers don't care to push the manufacturer to fix their nameplates.
Also: you need a receptacle within 25' of the disconnect, on the same level. There are disconnects with them built in, but I've always either used an existing outlet, extended an existing circuit outside, or pulled new wire in the conduit feeding hte disco.
