Shearer was better in the air. Better long distance shooter. Way better Free Kick taker (Kane's free kicks are abysmal). And potentially better holdup play. Except Free Kicks, Kane is great at all of this too.
Kane is a way better passer and had better linkup play.
Shearer is actually so underrated. For reasons similar to Kane actually.
That's all true, and Shearer was a brilliant striker too. I don't think he's underrated, though - many prefer him to Kane when his name comes up. And even though they had a cash injection under Jack Walker, Shearer was sensational at Blackburn, especially in SAS with Chris Sutton and being fed up Stuart Ripley and Jason Wilcox from the wings.
He was fantastic too, and what you mentioned is correct - better in the air and from long distance. Hold up play is much of a muchness.
The point is these players are the elite - Kane, Lewandowski, Shearer - so you can twist it either way to prove someone is better than another.
It's like Messi and Ronaldo - the only reason I think Ronaldo doesn't come close to Messi or Maradona is those two are aliens. It's not because Ronaldo isn't a brilliant player himself.
Just because I am advocating for Kane here, doesn't mean that Shearer and Lewa aren't among the best ever either.
I'd say Kane, Lewa and Shearer are all in the top 20-25 strikers of all time by anyone's measure. And, for plenty, some would be much higher than that. But that's a bare minimum. Though, tbf, maybe not as simple as it seems as there's a lot of great strikers in history.