You're saying it's the subtle things but then imply he's the reason we don't play a high-line? That's not subtle then. It's a bold claim, just like saying something like Lukaku's touch is the reason our defence is always put under pressure all the time. I kinda get what you are saying tho and I agree its about tactics, so do you not think Smalling would play higher up the pitch if he was told to?
In fact i think he thrives up there, especially if our attackers and midfielders attack with intent. When the midfielders are slow and the attackers lack movement, then Smalling isn't going to solve that, like Rio sometimes did. But when playing a high-line and our attackers push the opposition back, then Smalling is very good at winning the ball back and recycles it quick back to the forwards/midfielders to keep attacking. Both he and Bailly does this very well i think. Either with a header, or using their sublime pace and physique. Simple passes is enough in this situation. And this is a situation we should be aiming to archive every game.
When we dominate, he is really good for the team high up the pitch. When we ourselves is pushed back in the box, he is really good for the team. Im not disagreeing that his limitations has a negative effect on the way the team play, but i'm disagreeing that the subtle things is as detrimental for the team as you make out. How his lack of composure and awkwardness on the ball has a negative effect on the team is widely overstated. How his defending has a positive effect on how the team play is widely understated.
People like me in this thread probably come off as super protective of Smalling, and its because there's so many unbalanced opinions which either are exaggerated or just... not true.