Not about dropping the ball, but about making harsh tackles that can give away pens in the own box. A freekick in midfield is not going to hurt that much. Also if someone goes past him it would not hurt as much if there is cover behind you.
No point going over the top. Those players can still be good squad players under the right management. We certainly wants better starters, but right now our squad is not at the level City got and we got a terrible manager making everyone look worse than they would under a top manager. Still even City got lots of players in that squad that are far from world class. Walker is average, Stones is weak at defending, Mendy is very much up and down, David Silva getting old and so does Aguero. Pep makes them look far better though than they would look for us. If we got Henderson and Milner people would have slated them and wanted them sold too. Point is though a good manager can get the best out of his players.
This is not about Jones, but in general. I think we can certainly afford to let Jones go in the future. Although Rojo and Bailly are getting injured as much as him now. We need new players in first rather than selling anyway, but I would not waste more money on defense before we sort out our attack. In my opinion getting big attackers will reward you far more than central defenders will.