While your "suck line" (interceptions/sacks/fumbles) is a good indicator, you still need the eye test to confirm. Bortles should be at the Bottom 5 of any starting QB rankings.
Bortles numbers are pretty bad and he also only has 10 1/2 games. This started for me on the Saints board when I defended the position that Brees' suck numbers are deflated by the Saints having 11+ point leads for large stretches. He rarely is forced into throwing situations or situations where he has to hold the ball or force the ball in.
I used Bortles as an example. In the first 4 games of the year when the Jags went 3-1 and he was never really forced into a throwing situation. His line:
The next four games the Jags get blown out and he's forced to throw from behind. His line:
He was benched in one of those games also after two fumbles, or the numbers would be even worse. Over a full season that's 12/24/0 (very good) vs 20/48/12 (very bad)
For Brees it turns out the numbers are about the same in close games vs blow outs, so I'm thinking the spread might be a good indicator of how good a QB is. Great QB's perform well under all situations. Seems like an obvious statement, but then you have SI writing an article about Mariota that he had a good game against the Texans and quoting the traditional stat line 22/23/303/2/0. Mariota's suck line was 0/6/0 Not a good game, and failed the eyeball test for sure.