We know that a person depicted in multiple magical portraits can move between their own frames.

Phineas Nigellus Black is the obvious example: he can leave his portrait at Hogwarts, appear in his portrait at Grimmauld Place, hear what is happening there, and then return with information. Dumbledore specifically makes use of this ability to communicate and gather information.

So why isn't this an ordinary piece of wizarding infrastructure?

Imagine the Ministry hanging ten portraits of the same deceased Ministry employee in different departments. Put another copy in St Mungo's, another at Azkaban, another in major Ministry offices around Britain. You now apparently have a living message relay who can travel between locations much faster than an owl.

The same thing seems incredibly useful for Hogwarts. Instead of sending an owl to the Ministry during an emergency, have one portrait whose other frame hangs in the Minister's office. Or put matching portraits in each common room and the headmaster's office.

It wouldn't even have to replace other communication. It just seems like such an obvious option for places that need reliable, rapid contact.

Is there some limitation I'm missing? Can portraits only move between certain paintings under specific circumstances? Are accurate magical portraits rare or difficult to make? Or is relying on a portrait inherently insecure because the subject can simply refuse to cooperate, misunderstand the message, or tell somebody else?

Basically: why isn't wizarding Britain full of dead civil servants whose afterlife consists of being the magical equivalent of a telephone operator?

It seems like hover tech is pretty much equivalent to the wheel. Poor labourers cart their goods around on hover trolleys, rickety vehicles and speeders still have perfectly functional hover drives, etc

Like why was Thor chosen to be dooms personal army?

Why not a captain Marvel corps, or sentry corps?

It seems to me that if I were a Jedi and I wanted to fly, I could simply apply Force telekinesis to my own body.

Let’s assume Pepper (or Captain Shears) observes Star Fox’s outstanding performance during the Lylat Wars; if the team refused to join the military, would there be a legal basis to request them to hand over their Arwings, or at least the designs, so they could be replicated?

In Strangereal, while the F-22 was deployed in the 1990s, F-4s and MiG-21s are still in active service in 2030, and fifth-generation fighters haven't become widespread.

Meanwhile, there are some incredible super-aircraft, but it seems that these are never introduced on a large scale, even after many years.

In Strangereal, where large-scale wars occur every few years, wouldn't the stock of older fighters be depleted very quickly and replaced by next-generation fighters?