Height is not the most important thing in sizing a frame. Sizes can vary wildly for the same height depending on other measurements.
I'm not sure I would agree. Height (specifically from the seat to the crank) seems like it *is* the --most-- important measurement.
I think what you mean, or at least what I think, is that there are other very important measurements that can make or break your comfort on the frame as well. Having to large of a drop from the saddle to handlebars, to long of a top tube, etc etc can make a bike really uncomfortable to ride despite being the correct vertical size.