My two cents.....One thing to remember is that while Cardale did lead the team to the three wins at the end of the season, J.T. had a record breaking regular season. His compiled a lot of yards and TDs, that's not to say Cardale couldn't have done the same thing with all of the playmakers, BUT at the very least it proves that J.T. is capable.
Secondly, I think that J.T. is a much more natural leader than Cardale. Coach Meyer and various team members have voiced J.T.'s leadership abilities and that shows since he was voted as a team captain. One of the intangibles that is really important for QBs to have.
Third, (and this is a bit more subjective (because I haven't spent much time researching it) it seems like J.T. tends to be a better decision maker and distributes the ball better as well. I always seem to feel more comfortable when J.T. is making a read option or reading pass defenses rather than Cardale. But again this is a more subjective point from my perspective.
Lastly, I feel like the offense and Cardale do much better with a deep threat WR in the game, i.e. Devin Smith. Without that threat there's a lot more reliance on the run game and short passes where the QB must read the defense. And going back to my last point, I feel J.T. performs better than Cardale in that situation.
Sorry for the long post, but tried to put some thought into it like you asked. At the end of the day I'm not a coach and I hope the team focuses on the fundamentals regardless of the QB to produce wins.