Output in a virtual console (tty1) ridiculously slow; possible graphics acceleration issue

BTW, tty means any "teletype" device (serial line, pseudo terminal, ...). What you are talking about is the Linux virtual console. And scrolling on that is ridiculously slow, because recent versions of Linux use graphics mode in a framebuffer instead of text mode, but sometimes not graphics acceleration.

So check your framebuffer settings and see if you can't get it to use acceleration by using the right driver etc.

Edit: As one can see in the video, the problem is definitely unaccelerated scrolling by redrawing everything, one can see the "waves" as the content moves.

I'm also confused why first you seem to be using vesafb (which does slow unaccelerated scrolling) and then 2 seconds later inteldrmfb (which should do accelerated scrolling). Possible the problem is related to the switch. Please provide full dmesg output after boot, put it in a pastebin etc., and edit question with the link.