I still believe that asking yourself to have to stop what you are doing, turn, Look down, just to pull a knife out of the sheath is asking too much of yourself.
The same with replacing a knife back into the sheath when you are working on something.
Now for guys that only use their knife like once a week then that is a different situation.
For such people there is no point in owning a sheath with a design that allows a "no look" use of the knife.
But for other guys who work in jobs where the use of a knife is a common occurrence, then expecting them to need to stop what they are doing and deal with a sheath that needs that much attention is asking for trouble.
A real user knife, (say for a sportsman), needs to be a sheath that allows a guy to use it with confidence without having to stop and look at it each time.
I think this is why I don't believe in a knife sheath design that relies too much on things like snaps or Velcro that require two hands to operate.
Sometimes you dont have two free hands, sometimes you can't look down. Thus sheath design must be such that you dont take your life in your hands just because you are too busy to stop and look down.
Like the katana we use in Kendo, at first it seems crazy to try to put away a razor-sharp sword without looking at it, but with a bit of study you start to see how it's not that hard to learn how to do, and that in the end it is the best way to go.
So, this is also why I believe you are correct in thinking that a thicker learher is a very good idea.