I think the ultimate conclusion needs to be that Smalling is the best centreback we have. However, that doesn't necessarily mean he is good enough for a Manchester United side that wants to be challenging for the title. I'd argue he should still be worthy of a place on the bench, or our fourth choice CB, if only for his aerial ability alone (kind of like a reverse Fellaini to see games out), however that's something I think can be left open for debate. The problem then lies within recruitment in these positions. Can this be fixed in one Summer? Probably not. We'd have to sell two or three defenders and buy a couple of worldies and hope it all clicks, but I bet some fans would think we need to spend that money in other areas.
Smalling should be, and currently is, starting every week and it is on merit. I don't see this changing until we get a new manager who doesn't like him, or until we've had a few more transfer windows where we sign defenders that are either already proven to be better than him, or are bought as promising players who gel quickly and force our other defenders out of the side. However, those things have arguably already happened. New defenders were bought, rated higher, were younger and more promising, the manager left Chris out of the side, yet eventually it's him who's the only real consistent starter. The conclusion needs to be that this isn't an accident, so I'm always amazed to see the huge amount of criticism that Chris Smalling endures, especially from our own fans more than the opposition. Who do they want to play instead? Fail Jones? Marcos Crocko? Eric Barely? There are many players in our squad who need to go before he does.