Crawling all over an original, gives a better insight than a set of plans.
The basic problem is they are usually built by highly skilled people and well thought out.
Often when people copy, they do not understand every aspect of why and what material, and welding process & heat treating (some frames) was used. Then they try to cut corners (easier or dont have right equipment) and sustitute materials (cheaper or more available) and they end up with a destically different, usually weaker part.
A frame built badly can kill you, there are no shortcuts, moreso when trying for extreme light weight.
BTW, I am not dissing MECs work in any way, he is methodical, meticulous, well learned & willing to research what he is doing to the Nth degree, and is not willing to compromise in getting it right. That attitude however is not always present in a lot of people that, "Would like to build my own Frame"
I have done a fair amount of work for several framebuilders, and have a bit of insight into some of it. A guy I know stopped building his absolutely beautiful Alloy frames, mostly because of people modifying them or adding on to them, without re heat treating... bottom line is if he originally built it, it gets modded and screws up, its gonna look like it was his doing.. or his name gets dragged into the mes.