Leadership - Leadership is something a lot of people have an issue with. I'm honestly not sure how I feel about it. Are you saying that a player can't be great if they don't play a leadership role? I'm not sure I can accept that. I'd say if you were comparing two players who are, all else equal, you could say that leadership could put one on top, but as it's own point on grading a player I'm not sure how much weight it should carry.
Leadership is one of his overrated intangibles. Yes it's worth something, but it's immeasurable, and whatever impact it has doesn't narrow the gap between him and Kane.
Defense - The only way I can think of to measure defense would be +/- and blocked shots. For reasons I stated earlier I'm not sure of the validity of +/- and blocked shots isn't something I see tracked on either NHL.com or hockey reference so I have no way of judging defense without watching tons of Hawks games (which I don't regularly). So I do agree that defense is important in terms of measuring a player's skill and career, I just don't have a good way to measure it.
+/- is just about the worst way to measure defensive play, there are about 10k articles that explain the problems with it, and blocked shots don't make someone good defensively. Better measurements of defense include 5v5 shot attempts and xGF differential. Regardless, a winger has much less defensive responsibilities than a center, and Towes definitely excels in this area.
Going to the front of the net - I don't see how that's a measure of what makes one player better than another. Not everyone produces by being a net front presence. Also in terms of going to the front of the net, size often plays a role in that. I'm not gonna say that the 4" and 30 lbs Towes has on Kane makes it easier for him to play in front of the net, but it can be a contributing factor, or that's just Towes game and not Kane's.
Not nearly important as goal scoring, plenty of bottom 6 players do this well. The impact can also be measured in xGF.
PK - I'm honestly not sure what makes certain players good on the PK, its probably their defensive skills or if they're good on faceoffs (particularly if they're especially good in the D-Zone), but that seems to overlap with the defense argument above.
I'm not sure about Towes's priorities, that's just might be something I don't know about him vs Kane because I don't follow either of them that closely, but unless that's something that's specifically come out in the media, I don't think that's something one can objectively say.
You'll know good PK'ing when you see it. Toews is good at PK. Kane is probably not. And even if he was, he still won't play it because scoring is at a premium and you have your best scorers playing during the times that they need to score.
In summary, Toews has a lot of good aspects that are valuable to a team, including PK, defense, among other things. But all these features can be found in a 3rd liner like Jesper Fast. Scoring is at a premium and you can't teach that. If Fast scored 65 points a year, I'd still take Kane over him.