Okayyy bro it is your right to not accept figures posted on a forum by countless members. by the way GS engine is based on old GS450, GS500 engine architecture which is from the 80's. the engine used in sprinter is actually a scooter engine (look up suzuki flash) that was introduced in the 90s. I have both these machines and i've ridden the sprinter for more than 16,000KMs, for me it's always been above 50KM/L no matter how roughly i push it.
It's your right to disagree, as always. you can take a test ride of a sprinter/raider and find out figures for yourself.