if you look at our squad, you can identify a number of issues:
- we lack a prolific goalscorer
- we only have 1 legitimate winger
- our centerback partnership is really poor
- we lack midfield balance
ozil has nothing to do with any of those. the only scenario where it might make sense to get rid of ozil is if we decide we're either going to play 4-4-2 or 4-3-3. a number 10 doesn't really fit into either of those formations, though a 4-4-1-1 is basically a 4-4-2 and allows ozil to play as a support striker. even still, he is not the issue.
give him an aguero instead of giroud and he probably has at least 5 more assists this season.
build a better midfield behind him and he'll receive the ball in better positions and probably score more goals as well as providing his share of assists
build a stronger CB pairing and we probably don't drop as many points as we did and we're probably not even talking about ozil
those are 3 ready made solutions that would improve the squad as a whole. if you instead decide to sell the best player in the team, then you've now not solved the 4 issues above and you've created 3 more problems to try and fix.