To be fair, number of them won (for 90 minutes) is important, but it also shows only half of the story. The other half is the percentage of aerial duels won. Last season when they played together, Smalling was slightly better in that aspect, having a 65% rate, with Lindelof having a 62.7% rate. This season though, Lindelof has improved though, and had a 65.7% win rate which is higher than that of Smalling from last year (but lower than that of Smalling the season before that where he had a great 67.5%).
Nevertheless, they are close in that regard. And it isn't that Lindelof is not making headers, he won 96 this season, compared to Smalling winning 102 on his last season here.
So, as I said yesterday, stats say that there isn't much between them. I believe that Lindelof is less aggressive, so if Smalling was less aggressive, he likely would have had a higher percentage rate but probably still on sixties, which might have been a tiny bit better than that of Lindelof but not much (Maguire for example is far more aggressive than Smalling while still keeping his win rate above 70% which isgreat, Van Dijk is even better at 76% while being as aggressive as Maguire).
So really, stats-wise when it comes to aerial duels, Smalling is at best marginally better than Lindelof (counting Smalling's last season here, and Lindelof's last two seasons, I admit that Smalling was better before), and definitely is not the monster in the air some think he is. The difference between Maguire and Smalling is far larger than that between Smalling and Lindelof, is such difference exists in the first place.