People are being too general when talking about finesse pitchers and Hendricks. As usual I wont pretend to be a scout but from what I've read his change up is his only plus pitch. However, from what I've read historically pitchers with really good change ups and marginal other stuff have been successful because of it. Not all finesse pitchers fall into that category.
Logically, Hendricks is going to live or die by his ability to limit his mistakes. Thus far he's got a 1.46 GB/FB ratio. If he qualified that would have been in the top 40 pitchers in that area. His line drive rate against was 19.4%. That would have been top 25 had he qualified. His HR/FB rate was 4.9%. Had he qualified there that would have been top 5. His IFFB% was again top 5 at 14.8%. Put all that together and it suggests people are not making good contact. It's possible the league just hadn't caught up to him last year but there's no real way to predict that. Additionally, his numbers aren't really that far off his minor league numbers. LOB% is quite similar. Walk rate is a bit better but within the realm. His K rate is actually quite far down comparative to where you would expect after adjusting for the promotion. I would have expected more of a 6-7 k/9 based off his minor league numbers.
I've been on his bandwagon prior to last season because he doesn't walk players. It's the same logic as to why I think people are under rating Tseng. That being said, I think he's likely always going to be a good regular season pitcher but not really the guy you want in a 3 man rotation for the playoffs. His upside is likely Doug Fister who's a hell of a pitcher but who the Tigers also gave up as a playoff contending team. Hendricks will be efficient with his starts. He'll likely give you a lot of decent innings and save your bullpen. Anything more that is gravy. Keep in mind they sort of just paid Hammel $9 mil a year for that sort of production.