I don't follow college ball and I'm no draftnik. All I know about future pro prospects is what I hear from those professionals who do make a career out of closely following and evaluating them. And what little I know about any Giants pick is what I read and hear about them after the pick from those same professional analysts, as well as from the Giants FO.
Having established my (lack of) bona fides, I will say this--
Over the past 3-4 weeks Geno Smith has risen to a high profile controversy due to a combination of his abilities and achievements during his college career, and his very public reactions to the accumulative evaluations by these professional draft analysts. Their consensus before the draft, as I understood it, was that most considered him to be the best of the 2013 QB class, but just barely. There was also agreement that there was a strong likelihood that none of the QB prospects would go in the 1st round.
The fact that this prognosis applied to all the QB prospects--with the slight possible exception of Smith--yet Smith was the only one of them who felt compelled to complain publicly about the projections, was at the time a big red flag imo.
That big red flag only got bigger and redder as last Thurs night wore on, until Smith pulled an "Achilles" act and went into his tent to sulk Thurs night.
These events involving Smith lead me to a similar opinion of Smith that the OP articulates here.
Whenever I see Geno Smith in the media, I am not reminded of a future Brady, Peyton, Brees, Rodgers, or even of Ryan and Flacco, or Luck, Griffin, Wilson, and certainly not Eli.
When I see Geno Smith I cannot help but instead be reminded of Jeff George, Ryan Leaf, Jamarcus Russell. Big arm, lots of so called talent as a passer, extraordinary high self-opinion of his talent, but a monumental loser as a pro QB leader of an NFL team.
Of course we are all speculating now, and of course "time will tell". But if you observe human behavior over a long enough period of time, especially that of a particular group of people--like NFL QBs, for example--there are certain "tells" that reveal an early look at an individual's potential for success.
The Geno Smith "tells" are not very encouraging to many observers including myself.
Nassib's biggest weakness by far is his deep ball. He very often puts too much air under it and thus under throws it. If you're going to knock him for anything, it should really be that and not his handling of pressure. Since you didn't even point out the rather obvious weakest part of his game, it really makes me think you haven't watched him.
Nassib will get to ride the bench and work on the flaws in his game, whereas Geno may very well be thrown into the fire with the Jets. Plus Geno gets to learn from Sanchez as opposed to Eli. Nassib might not end up being our future at quarterback, but I don't think it is by any means a stretch to think he has just as good a chance of succeeding in the NFL as Smith.