I mean to me it breaks down into general categories:
Physical tools (arm, legs, size)
Mind (pre and post snap...absence of mistake)
Leadership (self explanatory)
Magic (Flutie or Eli or whatever...basically luck..but improvisation and FAvreisms play a role too)
Through my scale I'd give Fitz passing makrs for tools, high marks for mind and leadership, and I suppose failing marks for magic (not always his fault..Stevie...).
I suppose Trent would be passing in physical, failing in mind and leadership and magic.
JP high marks in physical tools and fails everything else, does not even receive marks in mind.
Fitz is pretty good, compared to what we've had he's amazing.