You're obviously not.
*waits for obligatory response explaining how you actually are a Hulk fan*
I'm obviously not a psychic.
If you've only seen the Hulk while he was a guest-star in other character's books, then I can see how you think he's best used as a plot device. If the "various comic book iterations" include his own title, then, apart from a couple writers, I don't see how you could view him that way.
Ah, nevermind.
I think the facepalm speaks volumes.
But since you asked:
* The Hulk is a character. When he is treated as such, you have room for growth and great characterization. Even the oftentimes wrongly stereotyped "Savage Hulk" had deep characterization under the tutelage of the likes of Len Wein, Roger Stern, and Bill Mantlo.
* The Hype (and other places) have tons of people clamoring for the Hulk in Avengers to speak and have more characterization than in his previous live-action appearances. Having him be a plot device would be diametrically opposed to those wishes.
* If the Hulk is simply a plot device, then, really, he could be substituted with any other plot device/generic character. There would be no need for the Hulk, specifically.
* One reason why many cite the two Hulk films as not performing higher in the box office/being more popular and/or endearing with general audiences is because they couldn't identify with the Hulk, himself. Taking away any characterization and making him a simple plot device would only further alienate those audience members.