I think the modern game has changed so much, especially the role of individual players in midfield. Traditionally, we've played with a midfield two of all rounders, contributing to all phases of play.
Now, especially at CL knockout stages, games are won and lost in midfield. To control the middle, I think you need a specialist DM who excels at ball winning and distribution from deep. Likewise a specialist box-to-box type to set the tempo, and someone to provide creativity.
I think that having all rounders is great, but you still need those specialist operators at the highest level who perform very specific and unique roles within the team, and I think midfield is an area where this rings true the most.
I think we're lacking both a DM and a box-to-box capable of dictating the game. Fred and McTominay are quality all round squad players but I just feel that they lack certain attributes (ball retention and creativity) to form part of an elite midfield trio (Bruno at the tip). For me, Zakaria and Verratti would be a solid pairing to fill those roles. A blend of aggression, physicality, ball retention, creativity and defensive awareness that would dovetail perfectly with a creative force ahead of them. Zakaria is attainable, Verratti probably not.
There are plenty of Zakaria/Ndidi/Partey/Casemiro etc who can all fill that DM role to an adequate level. For me, a Veratti, Arthur, Kroos, Modric, Thiago type player is usually the final piece of the jigsaw for most top teams.