As a glider pilot allow me a few remarks : pure Gliding ratios ( or Finesse max as we call it) in modern gliders can reach high levels but the most important other factor is the minimum sink rate and at which speed range it can keep that , That what is interesting, not the gliding ratio per se.
For info the ASH 25 ( which I sometimes fly) with winglets and 26m wingspan has a finesse of 62 with 0,45m/s and will keep a good sink rate through a large speed range. You will never get that sort of perfection in a jetliner because it is build for speed , not gliding.
A modern jet liner (e.g.B767, A330 B787 ) have "official" gliding ratios around or slighly above 20:1 but only at a very specific speed , outside of that exact speed, they will probably start dropping like stones, (i.e close to 10.1) . If I remember correctly the Gimli B767 got something like 12:1 with a Glider pilot at the commands.