I think the 2 main issues (from my POV) are:
1.
mental. He's struggled all year to trust himself to do the types of things he used to be able to do. Some of it is physical, like being able to generate his lift off his injured ankle, but the rest of it is just the fear that it will fail him again. I broke my lower leg a number of years ago and it took me more than 2 years to even start to feel like I could put the same stressors on that leg that I used to be able to, and I'm not a professional athlete. He's clearly struggling with the fear of having it fail on him again, which is why he's driving less and not going up if there's the risk of significant contact. He also seems to be a confidence person where if he misses a few shots he starts to worry about missing more and potentially "taking" shots from the many other players who need shots in this team.
2.
ensemble cast. The point I was trying to make in the other thread when I brought up San Antonio 2014 was that it's not easy for Gordon, or any of them other than Kyrie, to consistently average more than 20ppg in this team. Only Kyrie takes the volume of shots that you need to take to score 20+, and his ppg average has actually dropped this year. The rest of them just aren't taking the amount of shots per game to get to that number. Gordon is playing 26 mins, down from 36min in Utah, and taking 40% less shot attempts. His per 36 split is 15/6/5, which looks mediocre for a guy earning $30m. But where will he get his minutes and points from? Unless Boston starts scoring more than 113ppg, which is 13th in the league, and more than 118ppg, which is the Dubs at 1st, the points will have to come from someone else. And everyone, including Kyrie, and with the sole exception of Mook and Jayson, is averaging lower than what they were a year ago.
That's why I brought up San Antonio, because they had a spread of 8 players who averaged more than 9 ppg:
Parker 16
Duncan 15
Kawhi 13
Ginobili 12
Belinelli 11
Mills 10
Diaw 9
Green 9
As a separate exercise it would be interesting to see everyone come up with a hypothetical points distribution for the Celtics over the course of the season - how many people we expect each player to average, assuming we score 120 points per game, which would put us at No1 in the league ahead of GS or Milwaukee. There's not going to be many people averaging 20+ I wouldn't think
So I'm not necessarily using ppg as the main metric to evaluate Gordon. In fact if you look at his per-36 numbers, right now they're not far off his career numbers:
Season Age Tm G GS MP FG FGA FG% 3P 3PA 3P% 2P 2PA 2P% FT FTA FT% ORB DRB TRB AST STL BLK TOV PF PTS
2010-11 20 UTA 72 17 1218 4.2 8.7 .485 1.0 2.2 .473 3.2 6.5 .489 2.0 2.9 .711 1.2 2.9 4.1 2.4 0.9 0.6 2.1 3.1 11.5
2011-12 21 UTA 66 58 2015 4.8 10.5 .456 1.0 2.8 .346 3.8 7.6 .496 3.4 4.1 .832 1.1 3.1 4.1 3.7 0.9 0.7 1.9 1.9 14.0
2012-13 22 UTA 72 27 2104 5.7 13.2 .435 1.7 4.2 .415 4.0 9.0 .444 4.2 5.0 .827 0.9 3.0 3.8 3.6 1.0 0.7 2.1 2.1 17.4
2013-14 23 UTA 77 77 2800 5.5 13.3 .413 1.1 3.6 .304 4.4 9.7 .453 4.0 4.9 .816 0.8 4.2 5.0 5.1 1.4 0.5 2.7 2.0 16.0
2014-15 24 UTA 76 76 2618 6.7 14.9 .445 1.7 4.5 .364 5.0 10.4 .481 5.2 6.4 .812 0.7 4.4 5.1 4.3 1.5 0.4 2.8 1.8 20.1
2015-16 25 UTA 80 80 2893 6.5 15.0 .433 1.8 5.1 .349 4.7 9.9 .477 4.9 5.9 .824 0.8 4.2 4.9 3.7 1.2 0.3 2.5 2.3 19.6
2016-17 26 UTA 73 73 2516 7.8 16.5 .471 2.1 5.4 .398 5.7 11.2 .506 5.2 6.1 .844 0.7 4.9 5.6 3.6 1.0 0.3 2.0 1.7 22.9
2017-18 27 BOS 1 1 5 7.2 14.4 .500 0.0 7.2 .000 7.2 7.2 1.000 0.0 0.0 0.0 7.2 7.2 0.0 0.0 0.0 0.0 7.2 14.4
2018-19 28 BOS 43 16 1122 5.4 12.7 .425 1.7 5.2 .319 3.7 7.4 .500 2.8 3.3 .845 1.2 5.2 6.3 4.8 1.3 0.3 2.0 2.0 15.2
Career 560 425 17291 6.0 13.6 .443 1.5 4.2 .364 4.5 9.3 .479 4.2 5.2 .821 0.9 4.0 4.9 4.0 1.2 0.5 2.3 2.1 17.8
By no means am I saying he's doing fine and this is as good as we will get. Neither am I making excuses for him. It's clear he's still wildly inconsistent and he seems to be a confidence player in that if he starts missing shots and starts to think he's holding the team back and "wasting" shots that other players could be taking his performance deteriorates, he starts to become passive and takes himself out of the game by being hesitant. The deviation between a good performance where he scores 35/9/8 or 16/10/9 and a bad one where he scores 0 or 3 and takes 4-5 shot attempts all game is still pretty huge. We would certainly expect more from a rotation player, let alone a max player.
The challenge for him is to improve his efficiency, which is at its lowest point since 2013, as well as his FTA, which is half of what he was getting in Utah. If he shoots a bit better, is less afraid of driving into the lane and getting contact and getting fouls, his ppg will go up. His rebounds and assists on a per-36 are near his career highs. It's just that there's a limit for him, as it is for everyone, to consistently get to the 20+ ppg mark which seems to be the yardstick, based on his minutes and the way he is currently being utilized. We probably won't see him, or anyone else not named Kyrie, consistently get near that until next year and Danny decides to ship some players out.
In the meantime he has to do the best he can, be efficient with what touches he gets, try and contribute in other ways, and be prepared if it happens to be his night to shine. What I want to see is a confident Hayward, not afraid to take shots when they are there to take, not afraid to drive the ball, scores at a high efficiency, and is prepared to be unselfish to make his teammates better, so that they can score more points. Whether it means he scores 10, 15, or 20, or 30. I think his ceiling is still higher than most players on this team, other than Kyrie and maybe Jayson, so if he keeps doing that, then eventually he will win back his starting spot, which means more minutes and an ability to influence the game earlier, and get back to those numbers that everyone expects of a $30m signing.