Chains are efficient but to my thinking, no chain would be better yet! The GoldWing, for example, has a chain between the engine and trans, then there's the trans, then there's another chain leading to some gears that change the direction of power 90 degrees for the driveshaft, THEN there's the final drive gears which if hypoid really suck up power.
And all those whirling shafts on bearings! Sheesh. But yeah you're right about the smallness of the bike trans; small gearsets should consume less power than big ones.