To control the build up phase you need the first two lines to progress the ball vertically at a high level and hence the players you mention are absolutely crucial to how not only the build up functions but also how they control or contain the transition when the high press gets bypassed. If we had Van Dijk, Saliba, Keane and Scholes we'd be very close to having a team that could compete for the title. Arsenal and Liverpool haven't had world centre forwards but as a team they can and have scored a lot of goals because they have the ability to sacrifice defensive stability for goals.To control the build up play we need a team not just Scholes and Keane. To control defensive transition at much higher level, we don’t just need CBs who can play high line and Roy Keane. We need a team that doesn’t give possession cheaply. In summary, we can have van Dijk, Saliba, Gabriel, Keane, and Scholes, but it becomes not effective and will eventually putting us into risk of getting attack from counter if we have Hojlund and Zirkzee who constantly keep giving the possession away cheaply.
While I agree the big issue is midfield and defense, our attackers like Hojlund and Zirkzee who constantly giving away the possession are also a big issue. The whole team doesn’t know how to keep possession.
And for any team to effectively press high and play a more expansive brand of football, the CBs and deeper midfielders in tandem need to provide a high level of vertical passing threat in the build up phase and also thwart the counter in a high-line. This is what we fail to do and collectively the first two lines dictate how the game will flow. Even someone like Thomas Partey (Arsenal) would instantly be our best central midfielder because he provides a good level of vertical passing threat and is physically and athletically strong enough to eat up ground quickly which in tandem with Arsenal's CBs helps them control the defensive transition. Liverpool is another example I can use.
Your forwards won't be able to maintain possession for long if the aforementioned problems persist.