In the book, inviting bastards and lowborn to try and claim Seasmoke, Vermithor and Silverwing (plus Sheep Stealer and the may-not-appear Cannibal and Grey Ghost) was Jace's idea. Between that, and negotiating with Jeyne Arryn and Cregan Stark, you get the idea Jace was very much Rhaenyra's right hand man and somebody Rhaenyra could really rely on after Luc's death. Almost a pseudo-Hand before he named Corlys as Hand. You get the impression he would have made quite a good King if things had turned out differently, and is maybe only second to Daeron the Daring in terms of "heroic figures."
In the show, we got maybe 5 minutes of him with Cregan, nothing with Jeyne Arryn, and even one of his most significant moments, treating with the Freys, is presented as something he goes off and does on his own without Rhaenyra's blessing and it's unclear at first how she'll react. He's not the one to suggest Corlys as Hand, and it feels like the show is going way out of its way to push Rhaenyra and Mysaria, with Jace even bizzarely against opening the hunt for dragonriders to bastards and lowborn.
The dude doesn't have a lot of time left, and at this point it feels like they're going to have to do a lot of work to make what happens at the Gullet as impactful. Jace is supposed to be the guy who's different from Aegon and Aemond and Daemon, and I'm really finding the pushing of Mysaria (over Baela too for that matter) to be... annoying. Unless they really change the timeline around, we're talking the first couple episodes of Season 3.
(Sidenote, was supposed to be Forrest and Sabitha Frey? If so, that's... disappointing. Really having a hard time imagining her leading troops or having a thing with Alyssane Blackwood if so... she and Bloody Ben Blackwood and the Muppet Tullys made the Riverlanders be awesome in the Dance. I don't find it super-likely we'll get Blody Ben and Black Alys anymore... but maybe? Making Sabitha Frey old and focusing on her as a grasping politician is such a terrible choice because it just sticks with the "Freys are old political people" thing from Game of Thrones.)