Jehan is this version gets a lot of screen time because he actually has a functional role within the narrative. He is a plot exposition machine, if something is in need of explanation he is there to explain it to the viewer. Like how The Pope of Fools is crowned and Quasimodo’s deaf judge as well the implication what that means to the Parisian justice system which he doesn’t think highly of.
Jehan also in his capacity for explaining is a bit of philosopher in this version, more so than Gringoire. He has this whole speech on storming Notre Dame for the “People” as it just as excuse for people to horrible things in the pursuit of wealth.
He also doesn’t join the Court of Miracles, he just joins in impulsive as they are in the act because it looks like fun and the promise of treasure before he unceremonious stab by a soldier.
All in all Jehan is in keeping with his book counterpart as he is Frollo’s leech of a younger brother. He does has more of a role in this versions but he also means less to Frollo in terms of affection. Frollo just seem annoyed by his brother all the time and Jehan even mention that Quasimodo was a somewhat replacement brother. So Jehan has jealousy for Quasimodo for his brother’s affection.
Jehan’s character is never at the forefront of these adaptations so there is less expectation of the character, he’s not important and quite unlikable so while in this version he is in keeping with book he at least entertaining in this version.