I don't know how one can say a player is of a higher quality when you are comparing 2 completely different positions as in when you compare Lewandowski to Hummels or Subotic.
Cavani level players are 50M these days. That's why he hasn't already moved on. Napoli paid close to our record transfer fee for Cavani themselves. If you seriously think we will even make a bid for him then you will end up disappointed.
Lewandowski has all the hallmarks of a Wenger signing. Somewhat reasonable fee, technical ability, resale value and ability to further improve.