Its one massive component that is very rare to find in this league and in general these days since we're in the era of the 'cultured' ball playing defenders.
You overstate it's importance. Being "physically imposing" as you call it, in open play situations, is one of the key components of being a defender. You can have a similar effect if you can sweep up the pass before the final attacker receives it. Defending set pieces. Organizing the offside trap and back 4/3/5. Able to support a high line when your team needs it, without sticking out like an open sore. Being able to keep and pass the ball while being pressed, without hoofing the ball back to the opposition. Being a player that pressed players can use as an outlet.
You can't tell me with a straight face you think those pussies Otamendi and Stones are better CBs than Smalling.
City conceded the least amount of goals (27) in the league last season with the pussies Otamendi and Stones starting in central defense. They are on pace to concede 27 goals in the league this season, with Stones and Otamendi featuring in a good amount of games as well. They've conceded 7 goals from set pieces (one more than Liverpool) this season. We've conceded over 40 goals this season so far. Conceded more goals than City last season, even when DDG was in God form. Some pussies.
But as for defenders I put above Smalling definitively in the league, that would be VVD, the 2 at Tottenham, and Laporte. I would rank him in the same tier as Stones, Otamendi, Gomez, Rudiger... he's better than all of the above from a physical, "lock this forward down" perspective. Overall package? Doesn't distinguish himself enough.
VVD is better than Smalling because he's superior on the ball, they are pretty much very close in every other aspect.
Smalling is only VVD's near-equal when it comes to 1 on 1 matchups against forwards. In terms of the other categories I mentioned, VVD is ahead. Liverpool would concede more goals in an alternate simulation where Smalling was starting for them. Ironically, City would concede more with Smalling in the lineup instead of Stones or Laporte. Ditto with Chelsea. He would improve Arsenal's defense no doubt. Tottenham would see a negligible impact.
Smalling still has more big game experience and more impressive big game performances than any other CB currently playing in the league. Kompany is close and he's on the way out. You just have to see how well Smalling has performed against top 6 forwards. Kane, Salah, Mane, Firmino and Hazard havent had much joy against United when Smalling has started. He's nullified them several times. Only Aguero has an outstanding record against United. Hazard has only scored against United once with Smalling in the starting lineup and it was a penalty gifted by Jones.
I agree that his 1-on-1 skill is very very good. World class probably. But again, that's only one part of the package.