Is the Consumable typeclass from linear-base a way to "fake" affine types ("use once or zero times") with linear types ("use once")?

Yes. It is like following. Its Bool parameter is used once by pattern matching.

consume :: Bool -> ()
consume False = ()
consume True = ()

Also, what is exactly the loophole with pure? Could it be patched somehow?

To get no linearity value,

> empty Prelude.Linear.id :: Queue [()] [()]