As you seem to have realized, the thickness behind the edge is more important than the overall blade geometry unless you have something like a scandi grind, which is a terrible slicer. I have a large stable and have handled quite a few more, and I have observed this:
Spyderco USA made have thick edge bevels (note in the pictures above how large the bevel is to get to 9dps in the Endura above, or the linked 12 dps Para 2) ; the more recent USA production has gotten thinner. Japan production is a little thinner. Taiwan production usually has a thinner edge bevel than USA or Japan. Italy production Spyderco knives have thinner edges than the Taiwan production, making them the thinnest edge bevels as a group. However, by far the thinnest edge Spyderco I have is a Caly 3 ZDP-189, it is as thin at the edge bevel as an Opinel.
Benchmade older production had thinner edge bevels than Spyderco, but more recent production has gotten thicker.
ZT has thick edge bevels, similar to current USA Spyderco.
Chris Reeve older production was a little thinner than current USA Spyderco and current Benchmade. More recent production is thinner. So if you get a recent production 21 it should be pretty good.
I have an older Buck Vantage Pro that has a very thin edge bevel.
Too bad you aren't looking at traditional knives, they usually have thinner edge bevels and thinner blade stock than modern one-handers and are much better slicers. Most of them have lower-performing steels (1095, 440A, or some other cheap stainless), but there are few that have better blades (e.g., the Lion Steel Shuffler with M390, Viper EO with M390, or Enigma with M390 or US2000MC, which is the same as CPM-Cruwear). My Enigma in US2000MC is probably thinner behind the edge than any other knife I carry, and that includes Opinel.