I think Mat Steinmetz is one of the best, and stories like this always somewhat confuse me. As a 5' 10" rider on 175s, though that is not outrageous necessarily, I'd say it is likely to be the biggest thing holding you back from a world class position. As your fitter, I'd hope to see you off those for sure.

I convince very few people to go shorter. I simply guide them through an awareness building process, during which they get to choose for themselves. They almost always choose shorter. As a FIST fitter true and true, integrating cranklength selection into Slowman's brilliant fitting process was not difficult. The difficult part is the interuption of process that changing the length introduces. But there are ways to minimize that drawback, and really illicit quite an "a ha!" moment from many riders. You gotta use a fit bike to do this though, and you gotta use it correctly.

I am going to be presenting on this topic at the next FIST seminar next week. Hopeful to get a few more fitters off the "convincing" path and onto the "helping to perceive" path. I'll let you know how it goes.