Yeah they did. Even not that long ago.

I read some newer study someone posted not long ago that found that higher cadences were actually less efficient than slower cadences in many circumstances. That contradicts the commonly accepted wisdom of the last 20 years or so. We hear this contemporary idea that spinning is more efficient all the time, but watching this years TDF, I noticed quite a lot of the top climbers were pushing pretty big gears and not really spinning IMO.

Certainly when I started riding seriously, the mantra was: if you need more than a 42x21, you're off the back anyway. There was one semi coach that convinced me to 'build my strength" by spin climbing in the seated position in a low gear of 42x24 (!). For reference, local climbs over 1000 ft tended to average about 8% - typical of CA regional roads. I did it for a while, and it may have helped me overall, but it didn't really improve my climbing. Could always climb faster in a somewhat bigger gear. Nowadays I kind of think that different approaches work better for different people. Best to try a few ways and find what works best for you. I think it depends on both an individual's physique, as well as the muscle mix (fast/slow twitch).

WRT to the OP. I've always wondered about this too. Sometimes I run across strong runners, and they're really not that much slower. Some great answers in this thread. I'm going to go along with the 12% grade, maybe 13%. That sounds about right, based entirely on my subjective empirical experience.