Not to mention that to fly sailplanes one has to be able to manage the flightpath by handflying and managing pitch, roll and energy - understanding stall - and particularly how to recover from it - is a prerequisite because gliders don't have TOGA power.
A short comment from someone, who has done handflying for the most time in his flying life albeit a suitable autopilot was not available.
To compare handflying a glider in the heart of its envelope with handflying an airliner at the top of its flight regime as being similar or equal is far fetched. Aditionally the mental picture needed for flying a heavy against flying a glider is completely different as well. Therefore being able to handfly a glider does not qualify at all for flying an heavy airliner.
What does qualify is training with the specific aircraft in the required environment.
At the end of my military turn i started flying a PA28 prop, and nearly nothing of my previous flying hours helped me in doing so. By the way, my instructor had the same impression.