I agree. There's no doubt that the 'issue' is WAY overrated. Despite big claims by some, and amazing 'testimonies' by others, pros as still smashing fantastic times on normal length cranks.
I've thought of possible formulas involving a sliding scale -- percentage of inseam reducing as the legs get longer -- but who knows? All I've concluded is that tall people, most likely, should be using longer cranks that short people, but "how much longer" is obviously the question.
The 3 main advocates of long cranks have the same story: there are all tall guys who were frustrated in the old days by 175mm being the longest cranks they could get. So they finally got some long cranks, which felt great to them, then they make up some formula to suit their preferences and generalisations.
Kirby Palm got his 'formula' from, "a heap of short riders with 31-inch inseams used 170mm cranks", ergo, the magic 21.6% was born. I couldn't believe that's where he got it from. All those pages, and his formula is based just on that 'fact' and his personal preference. He knows
everyone used 170s at one time, so why didn't he believe that the guys with 32" inseams were suited to 170s, or the guys with 33" inseams? Etc, etc.
Another probelm with long cranks is that they are addictive; when someone first uses them they (often) immediately notice the extra leverage (especially off the saddle on short climbs), so become hooked,and find all sorts or reasons and new positions to keep using them.
When I first got on 180s (I'm only 6ft), I was like, "wow, the leverage", so I was hooked for about a year. I was so convinced that I had an advantage that I moved my saddle to all points of the bike to make them work, ignoring the fact that my knees were in my chest, I couldn't 'get on top of the pedals', and my hamstrings and medials were killing me. The day I put 175s back on my bike I felt like Superman
because I could get over the pedals and pound the **** out them
anyway, I forgot what i was talking about......oh yeah, stay out of my booze!!