The team is built for 3 at the back......because we don't have quality premier league centre backs. Not because of the full backs. People forget we've strengthened the FB/WB twice over since the Championship, yet our CBs are still the same (excluding a non-league CB we've added).
It’s not the 4 or 5 though. Plenty of worse teams than us (with rubbish CBs) can still be defensively solid playing 4s. It’s more the low block that bought our success rather than the number of CBs.
We played 5 at the back at Burnley and West Ham. Probably two of our worst performances of the season where we could have easily conceded 10 in those games combined. It was how we played not what formation we played.
I'd like to expand on these 2 posts.
Firstly, it seems too big a coincidence that 5/6 PL wins have come with a 5, I appreciate our 2 heaviest defeats also did. You could even argue the one win with 4 was more about circumstance, given the motivation post the Raul injury. Also nobody can convince me it was a planned formation change, it was a reaction to a lack of creavity. Neither Semedo or RAN were signed to play full back, so WB was the original intention imo.
All of our wide defenders can play both positions, but that doesn't mean the team can. In a 4 we still expect the full backs to push high up whilst the centre mids don't track runners - YW broke this down better than I can, but it's leaving the centre halves exposed more than would be the case with an extra man.
Boly is our best centre half defending one on one, but as we know he can have his switching off moments and to honest, parking his leadership, we'd be better off with Dunk or Mee than Coady at the moment. In a 4 he will have to be sacrificed sooner rather than later for a conventional centre half.
I also noticed that Semedo was making Dohertyesque runs inside Adama yesterday rather than both looking to take up the same areas, but Traore didn't look up and spot them. Improve that and we'll be more dangerous