Honestly, I can see Smalling becoming a class act. At his prime, Rio was arguably the best and most complete centre back I've seen, so I doubt that he can emulate that class. I don't really see any centre backs at the moment who are there. On a good day, Kompany is thereabouts, but ultimately lacks a little pace in comparison and has plenty of brainfarts.
Smalling doesn't make all that many mistakes; subsequently, I think you are far too harsh on him. As a centre back, he has mostly produced quality appearances with assured defending but ultimately lacking in finesse, compared to the likes of Rio. Compared to Vidic, on the other hand, I would say that Smalling's ball playing attributes are at least on par to what Vidic could produce when he came to United, and he did improve his game considerably during his stay; there is little to suggest that Smalling cannot do the same.
His red card isn't typical for Smalling, and thus we shouldn't be too harsh on him for that. It was a terrible tackle and a stupid first yellow; he can really do little but apologize for that.
Why does it go for a lesser degree for Jones than for Smalling, btw? Jones makes many more silly mistakes than what Smalling does and is often prone to brainfarts, unlike Smalling who is mostly solid in his defending. That's where your agenda shines through; you criticize Smalling for things that he rarely does wrong and lets Jones have a free pass. I agree on Evans though; he has too many mistakes in him for my liking, even though he is very competent on the ball.