You’re basically saying that .internal can cause frustration when it is used without good reason. Fair enough, but also not surprising. When it is used for the intended reasons though, then there’s just no other solution. It’s a trade-off between conflicting goals. “Simply do X instead” doesn’t remove the trade-off.
As a side point, there _needs_ to be something equivalent. People were doing all sorts of bad ideas before, and they had all the problems of .internal as well as the additional problems the hacks were causing -- like using .dev and then dealing with the fallout when the TLD was registered.
The biggest benefit of .internal IMO is that it is free to use. Free domains used to be a thing, but after the fall of Freenom you're stuck with free subdomains.
If `.internal` is for private-use only, they must be resolved by some sort of private or internal DNS. In that case, all domains are free for private-use anyway.
Unfortunately, that's not true in general. Google proved this with their handling of the .dev TLD. Security settings like the HSTS preload list can impact your internal network if you "squat" on a domain you don't own. Google added all of .dev to the HSTS preload list and now, if you use any domain under that, you browser will force you to use HTTPS.
