Rooney has played many roles and almost all his career, he was hardly the top man in many seasons. He mainly supported others. He played everywhere in attack while Kane has been an arrowhead all his life. Again it will be like a Hazard vs Lewandowski comparison.
Right, and what you've said here is why it's important to take a player's holistic contribution on the pitch into account, rather than player x scored more than y, player x is better. Hazard's role on the pitch was very different to most of the players he gets compared to, he was much more of a playmaker than a goalscoring inside forward.
Yes, that would be yo boy Diego Costa. Hazard had the same output performance in the league in 2014. They sign Costa (just off the back of beating Neymar, Messi, Ronaldo, Bale and Co to La Liga title with 27 league goals) and Chelsea magically win the league. The impact is clear!
Costa was excellent that season, they wouldn't have won it without him. Hazard was still clearly their best player that season, but opinions I guess and we can agree to disagree about who was the most important player.
What I won't ignore, is how bad your logic is here. "The impact is clear!" "Chelsea magically win the league" There's so much more to it than that.
Chelsea 2013 - 2014
Chelsea finish third, 4 points off 1st. They exit Europe in the semi finals stage. Hazard is their only player to hit double digits in league goals.
Chelsea 2014 - 2015
Fabregas joins, does brilliantly
Costa joins, does brilliantly (adds 20 league goals)
Matic has his first full season of English football, does brilliantly
Along with Courtois, you also have Terry, Cahill and Ivanovic having excellent seasons
Lastly you have Hazard, who goes on to win PFA player's player, Prem player, the FWA award, and the club's player award.
There was nothing magical about any of this. The club had a good season, and then went out and added some much needed creativity in midfield, an elite striker to improve on Chelsea Torres and an aging Eto'o, and some (especially second half of the season) excellent performances from a talented keeper and intelligent Mourinho moulded backline.