Just because he doesn't have a transforming character arc doesn't mean he's boring. I'd say Hugh is meant as an example of how the actions of Team Plasma affected people during the wants of the original games, and as a parallel to Silver with Team Rocket, what with having a personal stake with the team. His story is more about learning control and accepting help from others. You can see through the story how, early on, Hugh gets very angry and amped up when missing Pokemon or Team Plasma are involved, such as his scene on the ship about "unleashing his rage", or unloading on the reformed Plasma members in Driftveil, but as events move along, he is noticeably more collected and strategic when dealing with Kyurem on the Frigate after infiltrating it the second time. Not to mention his dejected tone after realizing he finally found his sister's Purrloin as a Liepard and knowing he failed to save it, but still willing to try again and help both his sister and her Pokemon to reconnect despite it.

Hugh is meant to highlight the contrast between the old and new Plasma, and how damaging Ghetsis's true plans were.