I think we end the season not knowing the ceiling on Gray, but we have a good idea of the floor.
Given the number of innings and starts he's made the past couple of years, I think he's a rotation regular capable of a pretty high workload. It may say something about current philosophy on the use of starters, but while 159 innings will not qualify for the ERA title, it currently is 44th in MLB in terms of innings pitched and will likely end up somewhere in the top 45- 55 among starters. This comes after 148.2 IP last year, so, over 2 years, he's 39th in IP. Good number of starts this year - 30 starts with the 6 man rotation the last two months.
The ERA relative to his FIP and strand percentage may indicate that the ERA should be closer to 5 than the hair below 4 we got this year. The walks remain a problem to work on. Even with the drop in K% he's not really getting better at avoiding walks. As for what happened to the Ks he's not getting, it looks like they turned into grounders, as his GB / FB ratio improved from 0.67 to 0.92. With improved infield defense (thank you, Dom, Candy/Vargas, and CJ's range), the extra contact didn't kill him.
He gets away with the extra base runners and contact a bit by being tougher to barrel up than league average and, for the most part, being tough to hit homers given the number of flies he gives up. He had a big drop in HR/FB this year, almost in half (18.6% to 11.5%, MLB average 15.9%).
Overall, the guy seems to be at least a back of the rotation innings eater or maybe even a mid-rotation guy if the defense is solid in the infield and he maintains the below average home run rate and the improvement in getting grounders. The next step I think would either be continued improvement in GB rate or a drop in the BBs. Do both and this guy is a #2 starter. Downside would be reversion to 2022 rates on HRs while maintaining a high walk rate. Then he's just a guy who can eat innings.
Frandsen I think has it nailed when he says keep in the lower part of the zone and throw the variety of pitches. This guy perhaps should aim for being a "crafty" pitcher.