: If you apply it to cycling (more strokes), higher (within limits) spin rates
: are more efficient, not slow "slogging".

I'll bite on this argument. In reality, its all personal, so hey, if you don't like them, use a euro. My two arguments for them are the cycling comparison as above. As a youth, I badly injured my knees from peddaling at a slow cadence at high gears (euro paddle) and had to switch to a high cadence at low gears (gp). It realy does make sence to use less effort more often.
My other reasoning trumps all arguments. My mostly out of shape wife used my gp once and is refusing to use the euro paddle now. She paddles longer and ends the day in less pain. She does not read websites or care about logic of this or that. She is a completely unbiased opinion and he uses what feels best which is a greenland paddle.
Scott