Here are their league records without penalties in the previous 3 seasons with teams league position included:
16/17:
Lukaku (7th): 18
Kane (2nd): 15
15/16:
Kane (3rd): 20
Lukaku (11th): 17
14/15:
Kane (5th): 19
Lukaku (11th): 8
You can see that in the past 2 seasons they have scored similar, but Lukaku has still had a great scoring record as part of a poor Everton side, whereas Kane has been banging them in playing in a side full of confidence and one last season that was involved in a title race for a large part of the latter stage in the season. Therefore, you have to take that in to account and praise Lukaku for that. However, Kane deserves all the praise he has been getting because his scoring record is top class. Goals to games you have to say that it is comfortably better than Lukaku's.
The 14/15 season was a poor season for Lukaku in the league, but more importantly the team. Stick Kane in our team in the 2 seasons prior to this one, and I imagine he would have a similar record to Lukaku in those seasons, or at least 14/15.
For me, penalties boosting goal tallies can have a big impact. Not saying they don't count, but they don't show the full picture when they boost the tally considerably which they have done for Kane this season with over 20% of his goals coming unopposed from 12 yards out.
Here is another example of 2 players in a struggling side:
Defoe: 14 goals. 5 penalties which means 36% of his goals have come from the spot.
Llorente: 11 goals. 0 penalties.
Both great scoring records for the sides they are in, but Llorente's is more impressive for me. Defoe scored 2 penalties in the same game.