I don't buy the idea that leg length has anything to do with the size crank you should get. From my viewpoint, if you generally like to ride at low cadence, then longer cranks might be desirable. If you like to ride and fast cadences then shorter cranks might be the thing.
Extra leverage IMO, doesn't compare to going to the next lower gear, however if you run out of gears then leverage is certainly some benefit for a moment or so before you either have to push the bike or make it over the hump.
With a 34.5 inch inseam, I've been quite happy on 165 mm cranks. Shorter cranks keep my knees from beating my chest to death when very aero and fast. I also like that it gives me a little more road clearance on my pedals for pedaling while in turns and clearance for road furniture and debris.
Granted, it's not a lot of difference, so preference I think is more what one is used to and not so much that leg length dictates adherence to some axiom that is still IMO sketchy after 40 some odd years.