I think, assuming he stays healthy, Z should have a better season next year for a number or reasons but all of them stemming from, it's the last year of his bridge contract.
There was as long a delay because he and his agent felt he'd shown enough promise to deserve more money and term.
Thus far, whatever the reason is, be it injuries, lack of development, lack of growth in strength and muscle mass, he hasn't shown enough improvement to be deserving of a raise. The production just hasn't been there.
I do think Trevor enjoys playing and living here and he seems to genuinely enjoy his teammates. But he's losing a lot of leverage to be able to argue that he's a key piece of this offense's youth core. Mac's game has turned a corner as the intended 2c for the future, Leo appears to be breaking out as the intended 1 C of the future, Gauthier is showing that he is on track to be an integral piece of the top 6 as a speedy winger with goal scoring ability and good two way play. Even someone like Colangelo is starting to perform really well and Sennecke is waiting in the wings. That's not to say Zegras' recent stretch of production hasn't been good in its own right. But add in Lacombe is trending towards superstardom, and we're in a situation where Zegras looks on track to provide more of a support role while younger guys than him are trending towards being the stars he, the team, and the fans were hoping he would be. And there won't be as much money when all of Carlsson, Gauthier, Lacombe, McTavish are paid, unless he earns it.
I agree that at age 24, Zegras still doesn't look strong enough in body and it might be contributing to his softer/less impactful plays with the puck. His vision, IQ, and skill offensively are still evident but he hasn't been as consistent as you'd hope he'd be right now. Next season will be a huge incentive to take his game to the next level. As much as might love his teammates and enjoy seeing them thrive, when it comes to career earning potential, next season he's going to be competing to earn a proper raise. He doesn't have much racetrack to build strength and get even more serious about his game, so I think he'll do it out of necessity. It'll be interesting to see how much that motivates him.