>The green screens tend to be much quicker and more responsive than the web frontends that are developed to replace them.
Agree! Back in 2005, I was involved in a project to build a web front end as a replacement for the 'green screen' IBM terminal UI connecting to AS400 (IIRC). All users hated the web frontend with passion, and to this day, I do not see web tech that could compete in terms of data entry speed, responsiveness, and productivity. I still think about this a lot when building stuff these days. I'm hoping one day I'll find an excuse to try textualize.io or something like this for the next project :)