Hi together,
I got my hands on the new I 20mm from Sigma this weekend. To me it looks "not bad" - but there is no Leica SL available to compare. In the corners its is better than my 18mm SEM till f-5,6 than it's equal on the SL. The bokeh (look for yourself) is like any super WA a little bit nervous for landscapes but f 2,0 is not so soft used in this field of Photographie. How good the intern Profile is is hard to say - you can switch it off in C1 but there is no C1-Profile available till now. In Affinity there are no intern profiles and than you have very strong distortion.
So look for yourself
1: f/2,0