Just to give you data points from another user:
1) SE 25.0.1, my config, hold down cursor down key, ada.e, 181 seconds (~10 lines/second)
2) Textedit, hold down cursor down key, ada.e, 186 seconds
When I use the mouse scroll wheel or page down in SE, I can get through the file (ada.e) very quickly. Page down is ~4 seconds, mouse scroll wheel takes me ~10 seconds.
My keyboard repeat in system preferences, keyboard, is set at the max slider location minus one tick. My delay until repeat is on the 'short' setting. I'm running catalina 10.15.7.
So then I did a key repeat test by making a new file in SE and holding down the 'a' key.
3) SE 25.0.1, my config, hold down 'a' key. 98 chars in ~10 seconds, still ~10 key repeat/second.
Then I changed my keyboard repeat to the max slider location, the delay between is still set to 'short'
4) SE 25.0.1, my config, hold down cursor down key, ada.e, 60 seconds, ~30 key repeat/second.
And to be complete, I did the open with new config you mentioned. This is with the keyboard repeat to the max slider location and delay set to short just like test 4.
5) SE 25.0.1, clean config, hold down cursor down key, ada.e, 60 seconds.
HTH