The Manning Effect
In my draft I could select a WR who ends up going to the Denver Broncos with Peyton Manning as a QB. There is a certain statistical privilege to playing with an elite level QB. Or say its a RB who gets to go play behind Dallas's dominant offensive line, or a pass rusher who gets to play with the Seattle DBs behind him making the QB hold the ball longer. The player I select for the Tampa Bay Buccaneers, will have a yearly statistical advantage in this favorable environment. (Manning as QB, Dallas Oline, Seattle DBs supporting them) I would even argue given that Tampa Bay has the first overall selection in 2015, the team for which my pick lands is often likely to land on a better team. This can be an advantage. Especially when my comparison comes down to yearly aggregates for statistics.
However, there are always 2 sides to every coin. Going to a weaker team, a rookie might start earlier, might get more defensive snaps and see more tackles. Might be used more due to being on a weak team which artificially pads the statistics. Or perhaps the DB I draft goes to Seattle and sees little to no snaps due to the talent and depth already on the team. Accumulating the stats over a four year period with year to year analysis I hope that the net effect is mitigated. There are advantages, there are disadvantages by for 'simplicity' sake and comparisons sake, I will not try to calculate the average yards playing with Peyton Manning adds to a WR per year and compensate for it...maybe one day.
Each offseason a team is provided with an opportunity to fill its needs through veteran free agent additions. This introduces a very difficult variable for Mock GM Draft. Say I use my first round pick on a dominant OT to protect the blind side in year one, while Tampa Bay selects a ball hawk free safety. In the first off-season (2016) Tampa Bay recognizes it needs a blind side protector and signs the top OT in the market. This is great for their team needs. Now my team has two high quality blind side protectors and a glaring weakness at free safety that the team is likely to never address in free agency as they have solved it in the draft. This process puts Mock GM Draft at a disadvantage as team needs will be filled in Free Agency for Tampa Bay and has a chance to refill a position I've already solved, BUT even worse is never approach the 'free safety' hole which my team has which forces my hand to address in the draft.
The Tape and Only the Tape
I love watching football, love statistics and everything that goes along with tracking a prospect from high school recruiting to NFL stardom. But after years and years of keeping up with it all, I realize there is more that goes into the process. 2015 is the perfect example. Watching Jameis Winston I see everything I want to see in a QB, accuracy, poise, anticipation, ability to navigate the pocket, a winning record (though he lacks the longevity I like in the college ranks). However, his off-field issues are well documented. I have no opportunity to dig into those to see how valid / scary those are in actuality. All I can do is go off the film. A players mental make up, their drive, their character plays more into their ability to succeed then any stats or accolades.
I am void of opportunities to evaluate character and work ethic. I stick to the tape and only the tape.