They both had stellar college careers, and neither has played a single down thus far in a real NFL game. THere is no basis to say one is clearly better than the other. THere is this notion that the college system a QB plays in matters. It doesnt. Yes, Mariota will have more of an initial adjustment than Jameis because of the system, but the initial adjustment is meaningless. They were both drafted to bad teams, neither is winning a SB, or even likely making the playoffs their first year. Two, 3, 4 years down the road, it is absolutely impossible to say who will be the better QB.
As of right now, there are 2 established starting QBs in the NFL that played for Urban Meyer, and none that have played for Jimbo Fisher. Alex Smith took a bit to get going, and certainly isnt great, but he is a quality QB right now. And Cam Newton didnt finish with Meyer, but he finished with Malzahn, who certainly doesnt run a pro style system. And no one would argue that Meyer or Malzahn, runs a more pro style system than Jimbo, yet, as of right now that system has more starting QBs in the league than Jimbo's system does. My point being, if a guy can play a guy can play. THe system you they play in college, has no indication of their pro success. Both Winston and Mariota can make any throw on the field, both are athletic enough to play the position, and I think both are intelligent enough to play the position. I think they will both have good solid careers to be honest, but to say one is clearly better than the other at this point is straight projection without evidence.
And who cares if Mariota graded poorly in that game, he wasnt running a pro system. He was supposedly highly impressive in workouts, and has been highly impressive in camp. Peter King said he was 3 years better than the schedule he had for him. With Mariota, there are no physical question marks, it is can he adapt to a different system. So far, which yes, at this point so far means little, he has adjusted just fine.