You take players based on what their grades are. Part of the grade has to do with physical ability and long term upside.
Every year alot of big school OL dont have the desired measurables or dont jump out to people on tape, they go later in the draft and it seems almost yearly some of them end up starting very early because they do come from the bigger programs, are well coached and/or come from pro style offenses.
Arkin is far more gifted physically than Nagy is, but Nagy received better coaching, played and practiced against better competition and benefitted from a quality weight program more than Arkin did.