Unless I mis-read or mis-understood you seem to invert the meaning of compression ratio half way through ?

> (100 / 200) = 0.5. Protip: compression ratios less than 1 are frowned upon.

> Unfortunately, it's not that simple. Say we had an algorithm (let's call it A) that, given any input whatsoever, was capable of achieving a compression ratio of strictly less than 1.