I think the answer to our midfield is depth in quality, and tactical versatility, and that we're pretty much there.
Simply put, options that can play in the system and last the season at the same level. To do that, you need depth, rotating efficiently so that the midfielders are not burned out by February.
Players that can serve different tactics, depending on the opponent. For example, not starting with Shaq in attacking/creative midfield if we need to be more controlled, but fielding him at the start if we need to be more attacking and dangerous, or during the game if we need to turn a game around. And vice-versa, taking out a more creative midfielder for a player like Wijnaldum or Milner if we need more control after a lead, etc.
Can depend on formation and tactics, on opponent, on result, on home or away double leg, rotation, form, and so on.
Fabinho-Wijnaldum-Keita seem to be the strongest 3 at the moment, but who can deny Shaq's impact - admittedly, a lot of people feel he can act best when subbed in and change the game, and I agree with that, but certainly there will be games where he'll start.
Fabinho's rise is being noted by many, and Klopp was patient like he was with Ox and it's surely paying off.
He's world-class in my opinion, and it will show more and more - at least by next year I believe it won't even be a discussion whether he is world class or not, but to me he already is now. Added to our world class mix of Alisson, Van Dijk, Salah and Firmino (I know it's very tempting to put Mane, Keita and Gomez in the mix, or even Robertson (!!!) but they fall just short at the moment, or still getting there in my opinion), 5 players of world-class level is the stuff of Trophy-winning teams, when in the right frame and playing style that can bring forth their qualities.
Fabinho's rise will be a new lease for Henderson in my opinion, despite people thinking it will mean his displacement from the starting XI.
Firstly, Henderson hadn't lasted a full season for years now, as lack of depth meant he had to play even if half fit at times, or without being fully recovered, which led to further damage. Now Klopp has the luxury of resting him whenever fitness is an issue, protecting him and making him more durable for the season (that's the concept at least). Secondly, it frees Henderson from the defensive role, and allows him to function further forward when fielded together with Fabinho, which is my preferred position for him, like in the earlier days. I think he'll need a bit of playing time to rediscover his game there, but I predict it can work wonders for him. Feel free to disagree, it's just my opinion and my feeling and use for the record, I am not interested in defending him if he's slated by anyone, I am aware he has a lot of critics, to which I don't totally disagree to be honest, but I value Henderson nonetheless and believe that in this new set of givens he'll benefit (and thus Liverpool will benefit).
Back on point, we have so many options now, especially once Ox returns:
Fabinho, Wijnaldum, Henderson, are the three that could be fielded to do a job deeper, with either of the latter two being the case if Fabinho is not fielded in a 4-3-3, or in a double pivot with Fabinho in a 4-2-3-1.
Keita, Wijnaldum, Henderson, Milner, Lallana, Ox being the 6 that provide the options for the 2 central midfield roles in a 4-3-3, in the shuttler roles, with Lallana of course not at his best at the moment just yet, and quite questionable whether he'll ever be again or whether we'll cash in in the summer and get a replacement, and Ox hopefully to return and be the player he was before injury.
But seeing the partnerships with Fabinho behind them in a 4-3-3, the combos of central midfield show how much depth in quality we have, and how much longevity it can give to our midfield in a season:
Keita-Wijnaldum
Keita-Henderson
Wijnaldum-Henderson
Keita-Milner
Wijnaldum-Milner
Henderson-Milner
Ox-Keita
Ox-Wijnaldum
Ox-Henderson
Ox-Milner
and that's before even adding the combos with Lallana (won't do it now, as you get the picture).
And finally, attacking midfield, where again a number of players can provide options. Lately even Firmino dropped deeper in a more of a #10 role, and while people do criticise the option, it may be some time before we see the benefits of this move, and maybe, just maybe, once again Klopp knows what he's doing and it's no different than when he fielded Firmino as a #9 and people had doubts. We'll see. But for now, I'm putting him in the options, as he is, de facto, an option for AM.
Keita, Shaqiri, Firmino, Ox, Lallana (with the latter remaining to show he can be an option anywhere, but putting him there regardless, I still remember what he can do if he somehow reaches his prior form).
Tactically, the factor giving us flexibility is that we have multiple players performing similar functions, so we won't be denied if a player misses out or opted out. The player whose qualities we'll find harder to replace if opted out in my opinion will soon turn out to be Fabinho, in my opinion, but still, we are used to being successful with other players doing a job well done in defensive midfield.
But, for example, Shaq is very efficient in a role performed by Ox last season, and when Ox returns, we'll have two options that can offer that. Similar with ball retention, passing, pressing etc., where multiple players can perform those roles, whether instead of one another, or even in tandem.
I think that these factors where the ones we were lacking last season, where we had to endure with Wijnaldum-Henderson-Milner throughout the season, with the only cover being Ox, who anyway needed his time to find his game in that role so wasn't really an option early on, and got injured before the end of the season so wasn't an option at the end either. And Lallana missing pretty much the whole season anyway. The triumvirate was less flexible, and utterly burned out too, and it cost us in every competition. Not because of their lack of quality, as so many people rushed to point out, but because of the lack of support, flexibility, and protection. The addition of Fabinho, Keita and Shaqiri, and the option of dropping Firmino deeper to field Salah centrally, as well as Wijnaldum upping his game a level, Milner miraculously still being as top fit as he ever was, and Henderson (yet to be seen, but my feel at least) being more free to play further up in midfield, changes all that, and makes us so much more competitive, on multiple fronts too.
So in my opinion, there may be a few more tweaks, whether minor or major, still to see, but midfield issue defined and answered by Klopp.