Barring injuries from this point on, it would seem we're likely to just field our senior players rather than the youngsters. With 3 or so games a month, rest shouldn't be a problem from now on.
Some have highlighted the problem with defence and attack, but I think the two are invariably related. When assessed in any particular individual way, our players aren't bad defenders in their own right. The problem is that for our system, a lot are not suited. We dominated possession in our games. This means that we're defending set pieces and counter attacks for the most part. Naturally, this means that we need defenders who are suited to a style where they will see a lot of the ball, distribute a lot of the ball, and then defend counter attacks and set pieces. That requires pacy, athletic defenders who have very good awareness and concentration, have good recovery speed and are able to leap well and make strong clearing headers. Similarly, they have to be comfortable on the ball, and capable of either passing across the back 3/4/5 but also making a forward pass to an advanced team mate, or playing a longer ball into the box or advanced wide area. I don't think there are many defenders who tick the boxes for everything, but a lot of our defenders don't really look like they tick the boxes for any of them. You look at who we've played at CB under JK :
Matip, Lovren, Klavan, Lucas, (Sakho in exile). You'd perhaps say that only Matip and Lovren are anywhere near good enough aerially. In terms of pace and recovery speed then we're deficient across the board. In terms of awareness and concentration, then perhaps only Matip definitely good enough. In terms of bringing the ball out and distribution, then again maybe Matip, Lovren and Lucas if we're being generous. They aren't bad players or bad defenders individually, but, Matip aside, they aren't well suited to what we are asking from them.
We could apply a similar bench mark in midfield. Again, we're generally playing 3 across the middle in more central roles. Defensively, we're asking one player to sit deeper (Hendo usually). This player needs to be someone who has the awareness and positioning to be able to snuff out counter attacks early. I don't necessarily mean fouling players. It could be just having the recovery speed to match the opposition attacker and then jostle them and get a challenge in or even slow them down long enough that we can organise. This situation where we see attackers dribble half the pitch, or that we get hit on the counter without a challenge is starting to become too frequent and is a sign that our DM's aren't cutting it. This DM player has to have the tactical understanding to be able to get to the 2nd ball from headers/set pieces/etc. That we often aren't winning these knockdowns and 2nd balls is also a concern that we aren't quite up to the task in this department. The consequence is that our defenders (who probably aren't suited to counter-attacks) aren't getting enough protection during counter-attacks, and that's probably enough to see us ship goals at an alarming rate (i.e. a lesser team will have 25% possession, and 2 chances, and end up with 2 goals from counter attacks or set pieces). On the ball, this DM has to be adept at distributing rapidly. We have a lot of the ball, and we have to generate tempo which means we can't dilly-dally on the ball with more than 2 or 3 touches. That means an assured first touch and then able to distribute very quickly either short or long distances, and not afraid to make an incisive pass rather than simply just "play the way your facing" and constantly knocking it about our centre halves or fullbacks.
The other 2 positions in midfield are freer roles. They can either be used to provide width or remain more central depending on what we're asking them to do. If they are remaining narrow, then it is absolutely imperative that these players regularly get into advanced positions, and are able to run beyond our strikers, and able to play 1-2s in and around the area. If we haven't already created some tempo, then they have to be able to manufacture this, either by being part of a slick passing combination (again requires a lot of movement on their part) or by being able to beat the first defender and make a key pass. Defensively, these guys need to be able to press well and in combination with the other forward players. You look at Lallana and Coutinho, and they do all of the above. Both are capable of getting into advanced wide areas (often do in fact) or remain narrow. Both are more then capable of making 1-2 combinations and slick interchanges. Both are able to beat a defender either with good close control, or through a deft turn. Both are capable of getting into the box (or near it) regularly enough to have a pop at goal. Both can generally press well and can often win the ball back for us. Neither Can or Wijnaldum do many of these things particularly well. Both are guilty of staying far too narrow. Both are guilty of sitting too deep (sometimes in the same level as the DM). Both are guilty of being far too static, and not making runs into advanced areas and creating some doubt in defenders minds (who should already be occupied by marking our forwards). Both are guilty of frequently taking far too many touches on the ball and slowing the play down, which kills any tempo (if there was any there to begin with). Maybe they are actually capable of playign the roles required but for some reason, we aren't seeing it.
It either requires a bit of tweaking as to how we set ourselves up, or to replace the personnel with players who are more appropriate. It is far easier to do the former, as you don't need to buy new players. You just need to be able to figure out the strong and weak points in the team, and then construct a system that will utilise those strengths and mitigate the weaknesses.