My basis would be quite literally all of bike forums convincing me in a unified manner that spinning is more efficient until I tried it myself and adapted my cadence style. I tend to ride in a style that mixes between the two, but can spin close to 120rpm for short bursts. This is by far the most power I can produce (up to about 465 watts) ,
Baby spins at 60 rpm is either for old men or for warming up.