Leadership, playing defense, going to the front of the net, penalty kill, should I go on?
First of all, I'm not say that stats are the only thing that matter, I was just asking what else you thought goes into it.
I'm going to try and address each of your points one at a time.
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.
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.
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.
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 know this sounds cliche, But Toews has always prioritized winning over stats. Kane has higher highs and lower lows, Toews has been more consistent. They are both great, and I don't know that answer. I kind of feel like there is some Kane bias because he is the American, But i also recognize that when at his best, he is/was in a league of his own.
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. The highs and lows argument is an interesting one and I'm not sure there is an answer as to what's better. As for there being an American bias for Kane, I'm not sure that exists (but I can only speak from my personal experience), I've never felt it.