Unable to comment on any of these as I don't have reputation on meta
The new fonts are GRIMgrim on Mac Safari+Chrome,Safari + Chrome - really terrible.
Sorry - but the system UI font is just that: for my UI. Not for reading lots of text at speed. I can genuinely feel myself reading slower with the system UI font as compared to Arial.
Yes, I realise they're both sans serif, but the UI is more difficult to read than Arial, end of. Maybe it's the small inconsistencies in Arial that means it's easier for the eye to "grasp" the text; much like ragged-right and that weird dyslexic-friendly font are both easier than pretty much any other layout or font.
Basically - the more rounded / consistent the font is, the more difficult it is to read at speed. That's why serif is consistently quicker to read.
I'm not coming here to look at pretty text,. I'm coming here to quickly get answers to stuff, and the speed at which I'm able to read the text is therefore very important.
(I am unable to comment on any of these as I don't have reputation on meta.)