One likely positive factor in a potential deal is that we seem to have gone in very early with Neves. By all accounts, he’s been identified a long while ago and we’ve likely been speaking to him/his people, communicating our vision and making the player feel wanted.
He does look a great CM in the making. I don’t worry about Mainoo at all. It’s like saying Barcelona are only allowed to have one of Pedri and Gavi. If it works, the true strength of the pair will come when the two are paired. Both players will bounce off each other, play triangles and develop a telepathy due to similar wavelength.
We are now in the midfield 3 era, so the third midfielder can be used to compliment the pair in different ways. A midfield of Mainoo/Neves + 6 would be applicable for certain games, and a midfield of Mainoo/Neves + 10 would be applicable for others. Both players do more than their fair share of defensive work for the latter scenario, and both have enough creativity for the former set of tactics. In a squad, you want to have about 6-7 options where all profiles are covered in midfield. A specialist DM and a specialist 10, who can also play out wide and will thus get games in both roles across a season would compliment them. A player like Eze, for example, would be great with them, as he’d play ahead of them as the 10 at home to Forest, and could play on the left ahead of them +6 away at City.
And all of this is before considering that we don’t really know which role Mainoo will take long term anyway, as he may well simply just be a DM himself. I certainly think we need a physical DM, but I wouldn’t be against Neves as a DM can often be bought for cheap with effective scouting. There are always loads of strong players who can cover ground and win duels. Fofana at Monaco for example has been linked, and is out of contract in a year I believe. Adrien Rabbit is out of contract this summer. Then there are others on the continent like Gourna-Douath or Mandela Keita who can probably be signed for less than 20m on low wages. Players like Bissouma, Sarr, Baleba, Kamara etc will always be available for 20m or less.