allen will never be great due to the fact that he is inaccurate.and he doesnt see the D very well--hence the checkoffs which practically get his receivers killed. he may be good to very good because of his athleticism,winning frame of mind,size and toughness.
darnold is a question mark. his problems are more mental....the turnovers.He MAY be able to grow out of that.Although I dont think that can be so easily unlearned.
Mayfield--altho short(not that short) is tough,can see the D , has a nice(not tremendous) arm,makes quick decisions and is accurate.