Stretch -> Buster = Shot Fonts

[Sam Smith]

After upgrading from stretch to buster, I was left with some fuzzy fonts 
on the built in KDE terminal (Konsole). I documented the painful 12 hour 
discovery process here: http://www.net153.net/blog/20190318-shot-fonts.html

This is the new engine: 
http://www.net153.net/pics/shot-fonts/Screenshot_20190318_170153_org.png

And the old: 
http://www.net153.net/pics/shot-fonts/Screenshot_20190318_170259_mod.png

Yes I am aware of the new engine in libfreetype: 
https://www.freetype.org/freetype2/docs/subpixel-hinting.html

as well as a previous bug: 
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=866685

But I find it odd that the "new and improved" engine has in no case any 
examples of improved text and the only fix is to simply force the old 
engine into use.

I figured I had to be missing something, hence spending nearly two full 
days on the matter. But I can find no way to make fonts using the "new" 
engine to look any better. Even stranger, if I force the use of the 
freetype 'autohinter' instead of using the default 'native' hinter 
(which all docs state not to do btw) then mostly everything improves.

I've got to be missing something here but I'm out of ideas. The only 
thing I haven't really messed with is if there is some kind of DPI 
mismatch in my system but not sure how to check that (and too tired to 
mess with it now). Any other ideas? I'm actually quite happy with my 
fonts now using the 'autohinter' and turning on subpixel hinting. But 
certainly the freetype author didn't just break fonts for the entire 
world and the only thing we say is "just use the old engine"???

Regards,