He wasn't "trust into the role" (sic). He was the only slot receiver behind Godwin. He played over 50% of the snaps in nine games this year. He was in to block on many plays and in others he was the third or fourth option. He was awful in that role. Missed blocks, dropped passes, lazy route running, and mental mistakes to the point that Brady was frequently yelling at him. He was bad and he's not going to last in the NFL as anything beyond a depth player.
Brady is known for throwing to his third or fouth option if he has a mismatch. He still didn't go to TJ. Brady would have thrown to him all day long after Godwin went down if Johnson didn't drop 40% of the passes that came his way.
First off, let me say that TJ wasn't great this year.
Second, TJ was never a 3rd or 4th option. Goodwin, Brown (when he was there), Evans, Gronk, and Fournette were OBVIOUSLY higher priority than him. When Fournette was out, so was Giovanni Bernard. Implying that someone was 3rd/4th on the depth chart at WR and therefore was 3rd or 4th option for Brady is just not realizing that while Tom spreads the ball around, he does it to multiple positions. The 3rd and 4th WRs that have played with Brady have always put up really low numbers. Here is a break down:
Third, TJ's stats were inline for just about every 3rd or 4th WR on the depth chart in Tom's career. I'm just going to start in 2010.
2010:
3rd WR: Brandon Tate 24 catches 432 yards (catch % of 52.2)
4th WR: Randy Moss 9 catches 139 yards (catch % 40.9)
2011:
3rd WR: Chad Johnson 15 catches 276 yards (catch% of 46.9)
4th WR: Julian Edelman 4 catches 34 yards (catch% of 44.4)
2012
3rd WR: Julian Edelman: 21 catches 235 yards (catch % of 65.6)
4th WR: Deion Branch: 16 catches for 145 yards (catch % of 55.2)
2018
3rd WR: Chris Hogan: 35 catches 532 yards (catch % of 63.6)
4th WR: Phil Dorsett: 32 catches 290 yards (catch % of 73.2)
2019
3rd WR: Mohammed Sanu: 26 catches 207 yards (catch % of 55.3)
4th WR: Josh Gordon: 20 catches 287 yards (catch % of 55.6)
Tyler Johnson: 36 catches 360 yards and (catch % of 65.5)
Tom Brady used Tyler Johnson about as much as he typically uses the 3rd or 4th WR on the depth chart. Tyler Johnson caught the ball at a better rate than most of those guys throughout Brady's career.