If you have to configure the host to support the client rather than the client supporting unknown existing hosts, then what you have is a terminal, not a terminal emulator.

In 1970 all terminals were their own thing, tied to a single host somewhere in the same building by a dedicated serial cable. The terminal didn't move or connect to random other hosts, and the host had to be specially configured to work with any terminal connected to it.

Since then, a few terminal definitions have become standardized across all hosts for decades, and terminals are emulators that emulate one of those 40 year established standard definitions, because today terminals connect to countless unknown new random and varied hosts that the terminal user didn't install and configure before connecting, and may not even have the admin rights to do so after the fact either, and even if they do, it's wildly and inexcusably awful to require that.

It's entirely backwards for a terminal today to default to asserting it's own new $TERM, and to characterize the problems caused by this as "the user forgot to do this totally unreasonable thing" that no other terminal or terminal emulator has required for 40 years.

It's 100% a bug. The fact that it's intentional just means it's a design goal bug.