Last season, a lot of goals were shipped because people dropped their level. We can certainly blame the central midfield for some of those goals in the first half of the season, when opponents got a free reign to run into the box, but a fair number of goals were also caused by guys not checking their blindspots, or heck - even what was ahead of them.
Goals at the far post when attackers ghosted in behind the likes of Johnson / Wisdom, goals in the middle when Skrtel and Agger fell asleep instead of tracking attackers running into the box, goals that went in because Reina couldn't dive low on his right anymore, goals from corners because our keeper / centrebacks didn't coordinate better on assignments.
I'm kinda' mixed about our defence actually - better quality is definitely useful, but I'm also wondering if we could actually still run with the current defence if we could just squeeze out an improvement in attitude and effort. I'm all for buying to upgrade, but if we didn't, I don't think it's the end of the world if - and that's a big IF - we could make sure the silly mistakes from last season are minimized.