Not sure I understand your concerns. If you have DirectX there then you will have the same GPU rendering.
If that's about CPU rasterizers then Direct2D/WARP and Skia rasterizers are pretty good.
Problem is that if you have two monitors of the same size but one of "standard" 96ppi and another is, say, Retina grade (300+ ppi) then GPU rendering is the only reasonable option. Number of pixels to rasterize is 9 times more in Retina case. We do not have CPU performance increased 9 times...
Editor keeps each line in separate <text> DOM elements (like <p> but no margins and only text inside).
So we just need to relayout one particular line in order to show typed character.