Well there’s a difference between the unit and the individuals that make it up. I’m talking more about the unit.
I’m pretty happy that we know how to defend as a team. The problem is we don’t know how to attack.
Leaving aside for a moment that I am less convinced of our defensive prowess than you, let's look at the limitations in our attacking play.
1) Would they be immediately improved with the arrival of a new RB?
2) Would they potentially be improved if our CBs didn't have to sit so deep (due to their own lack of pace)?
The unit *might* be better at defending than I believe - I'm happy to leave that point. But the same personnel within that unit are part of the reason we struggle to attack. If we do nothing to change the personnel across the back 4, we remain completely reliant on the midfield and forwards to attack. Succes in modern football however demands that fullbacks contribute regularly in attacking play, and that CBs can at least move upfield with the ball at pace IF there is space to do so. Additionally if the CBs can play higher up the field when we are in possession, we can then have the midfield move further upfield in immediate support of the forwards.
I'm not saying we don't need to recruit better midfielders - I am firmly of the belief that we should be buying two new central midfielders this summer ( a DM and a box-to-box), and it's glaringly obvious that we need upgrades on Iwobi and Bernard in the wide midfield areas. I'm not saying we don't need another wide forward / winger - we clearly do. I am just saying that our defence needs addressing too.
Until all those areas are addressed the current squad is not good enough to put out a full first 11 without any glaring weaknesses, even if everyone is fully fit. All that being said, we're still in with a chance of finishing 6th (above Arsenal and Spurs) with three games to go, with THIS squad. It's absolutely mad to suggest that Ancelloti has in any way underachieved with this club.