Every manager that has been there since the buying binge began ended up doing that sooner or later. It's the problem with too much of an embarrassment of riches coupled with the expectation of lifting a major trophy every time out. Some seasons, you need to reload so you don't end up rebuilding later.
I suppose they're thinking that if they get it together at the back, sooner or later the attack will take care of itself. One thing that can be said for Potter is that he got the club playing progessively better defense every season without needing big-money 'ins' to do it.
I agree with the consensus that it's a poor fit. Potter has never managed egos like this, or been in this kind of fishbowl, and those are very difficult skills to learn on-the-job.