Dear Louis,
Again we have a misunderstanding :
I use the definition 'line'-input/output when the levels are about 300 mV. (mic-inputs have a level of about 3-5 mV)
Sometimes I too perform using a 5 meter cable to my stagebox, followed by a 25 meter multi-cable and at the end a mixer..... without problems.
During the 35 years being a 'musician' and electronic engineer I never saw organs or keyboards with balanced outputs..... and believe me I saw/repaired/modified/owned many !! (Korg, Roland, Wersi, Hammond, Technics, Solton, Ketron etc.)
By the way : It's my birthday today ! (47)

Sure I see your point but I still don't see it as a real flaw..... I'm sorry for that.
Roel