The speed is much much better in the current release.
I had a read through that thread, I don't think the project was against the functionality, but wanted APIs internally for it, which included APIs for pausing output and keyboard control and selection from the keyboard.
So while the implementation in the patch may have been rejected, at least one current bug is open on the VTE gitlab
https://gitlab.gnome.org/GNOME/vte/-/issues/588