In the 90s , I wrote Windows C++ software that talked to hundreds of different 3270 applications in a very difficult attempt to screen-scrape them and display the data in a modern windows UI. It was difficult. Then take user input and submit it as a form back to the 3270 application.
It would have much easier if the applications were TTY line-based.
In 2000 and 2001, I used software like that ("TSS") as a customer service rep for MBNA, which has since been bought out by Bank of America.
It was incomplete, as anything offering a WinForms GUI over a 3270 client would necessarily be, but still very useful. A 3270 terminal emulator was also available; most folks quickly learned to use it for tasks the GUI didn't support, and some of us ended up preferring it for some tasks the GUI did support since it tended to be much more accommodating of muscle memory.
In retrospect, it must've been a real engineering challenge to integrate with a 3270 client whether via screen-scraping or the wire protocol. Like HTML, but with structural information only designed to be parsed by the terminal, or in the screen-scraping case with no structural information at all.
On the other hand, it couldn't have been WinForms since that debuted the year after I quit that job, so maybe it's my recollection that's somewhat faulty. It was a long time ago!
It would have much easier if the applications were TTY line-based.