As I've established in other books, "contact specialist" is basically what Deanna Troi's job was when she wasn't being a counselor. It's an officer who's an expert in alien societies, xenobiology and xenosociology, diplomatic protocols, and the like -- not just for first contacts with new species, but really for any diplomatic interaction with non-Federation cultures. I don't see how that's limiting. (And part of the fun of T'Ryssa's character is seeing someone so basically undiplomatic having to learn to be better at diplomacy.)
It's just that the TNG books post-Destiny
have tended to focus more on politics, either within the Federation or with well-understood neighbors. Which is a somewhat atypical focus for TNG, at least when it's such an exclusive focus. Yet even so, T'Ryssa did get to do her job properly when she went to the Kinshaya's (new) homeworld in The Struggle Within
, and as part of the contact mission to the Machine in Cold Equations Book 3: The Body Electric
. She played an important role there in keeping with her specialty, since she was the one who identified the Machine's origins based on her knowledge of Starfleet history.
Agreed, the use of Chen is more plot device than anything else and so people don't want to buy into her character (except for being the annoying pre-teen younger sister!)
By "people", you mean yourself. Please don't be afraid to own your individual opinions for what they are. Over the years, I've heard more praise for T'Ryssa Chen than criticism, although not overwhelmingly more. There's nothing in Trek fandom that "people" as a whole uniformly agree upon.
After all, as I said, we've seen the same plot device used with Sulu, Chekov, Worf, Geordi, and others, and yet that didn't keep "people" from buying into those characters. (Spock too -- he went from science officer to captain to ambassador.) So your statement here doesn't even make sense. If you don't like her, fine -- you're entitled to that opinion. There's nothing wrong with that. But it's your own opinion, not a universal law.