Harsh.
Keane has probably been our best defender since before Silva was fired. He definitely had a shaky start and for the first 12-18 months I was not convinced, but he settled down well and proved his worth. That's not to say he's irreplaceable or that we couldn't find an upgrade. I said recently in another post he is the player I'd look to sell given his age and profile and the fact he is probably our most valuable defender that we could sacrifice. He had a bad game against spurs, but to say he's not been decent for the majority of season and certainly the 2nd half of last at least, is revisionist.
Mina too has been reasonably solid this season and has on occasion out performed Keane. He is not as consistent as Keane, but I think by upgrading Keane you would in turn get more out of Mina, as he seems to be a defender who very much relies on a stable partnership and leadership. While Keane has for the most part been a solid and dependable defender, his lack of speed and occasional off day hasn't always provided the best cover for Mina to flourish. Not saying we would get Koulibaly, but if we were to sign someone of that ilk, I think you would see an extra level from Mina.
Holgate has shown in glimpses what he is capable of and what his ceiling could be. His biggest problem for me, and this goes for the majority of our defence and probably spreads to the rest of the team in general, is that we have rarely if ever had a consistent run of games without considerable changes in both personnel, formation and tactics. Holgate has played several positions, several formations, had several partners, as both a 2, 3 and even the effective 4, and has generally been decent. Last season he showed his ability bringing the ball out of defence and his calmness under pressure. This season, he has been caught out a few times. But he is still young and still learning. There aren't many 24 year old centre backs who are the finished article, and those that are cost a premium. They probably haven't been shunted around the starting 11 and in and out the side either.
Godfrey I agree has been immense, his pace and power are another level, and his aggression is something we've missed for a long, long time. But he has had his moments in the heart of defence as well, and he looked shaky early on playing RB, let's not pretend differently. His best form has still been at LB, and as part of the back 4 unit that served us so well for those months when Digne was missing. The main thing to take from that, is when that was the case, it was a consistent and settled, tried and tested back 4 that played that system, hardly any changing.
The biggest issue has been that lack of consistency since then, and the chopping and changing has led to an imbalance. This has largely been down to a series of injuries and having to make do with what we have, as well as some criminal over exposure from a decimated midfield unit.
Getting rid of everyone because of some inconsistent form in an often bizarre and hectic season is akin to throwing out the baby with the bath water. Can we improve? Yes. Does it need a complete overhaul, selling players at way below their collective market value to do so? No.